Mack and Lindsay Saunders had different opinions when their oldest son, Scott, decided to return for a second semester to Colgate University's History Study Group in London.

''I was all for it, absolutely,'' Lindsay Saunders said from the family's Lower Macungie home. ''He loved England. He loved travel. He loved history.''

Mack Saunders asked Scott to spend his senior year on the school's upstate New York campus. That way, he would be better able to decide what to do after graduation.

''I urged him not to go,'' Mack Saunders said.

But, he added, ''The thought of terrorism never entered my mind.''

One year ago Thursday, Scott Saunders, 21, academically gifted and hoping for a career in law or journalism, was among 270 people killed when Pan Am Flight 103 exploded over Scotland and crashed into the village of Lockerbie.

A Semtex bomb with an air pressure-sensitive detonator had been concealed in a suitcase. The leading theory is that the suitcase had been transferred to the Boeing 747 in Frankfurt, West Germany, from Air Malta Flight KM180 in violation of international regulations, since it was not accompanied by a passenger.

The Popular Front for the Liberation of Palestine-General Command is suspected of building and planting the bomb at the instruction of Iran.

Scott Saunders, a tall and handsome Emmaus High School graduate returning home for Christmas, was a random victim of international terrorism.

As they learned the facts, the Saunders and other relatives of Flight 103 victims became convinced their loved ones died as a result of slipshod airport and airline security. They were appalled by the U.S. government's apparent unwillingness to investigate why warnings of an impending terrorist bombing were ignored.

Outraged, 250 relatives of Flight 103 victims met in Hasbrouck Heights, N.J., Feb. 19. Few among the predominantly upper-middle-class crowd ever had been activists, but together they launched a crusade. The result was Victims of Pan Am Flight 103.

Before the meeting, Mack Saunders and Bert Ammerman, an assistant high school principal whose brother was aboard Flight 103, hurriedly drafted a preamble.

The four points - emotional support, improving airport and airline security, a government investigation and changing U.S. policy to allow no terrorist havens - remain the group's guiding principles.

Today, Victims of Pan Am Flight 103 is feared and respected in Washington as unrelenting, well organized and savvy. As president, Ammerman said he speaks four to five nights a week and works eight to 12 hours Saturdays and Sundays.

Ammerman's commitment is not unusual. At least 25 other Victims members work as many hours. Saunders, 50, will retire early from AT&T Dec. 31 and, in all probability, return to the Victims board of directors as treasurer.

''It's become an obsession, a commitment,'' Ammerman said. ''But we've seen success so we'll keep doing this.''

Months of intense lobbying persuaded President Bush to appoint an investigative commission Aug. 4, after he initially rejected the request April 21.

Monthly meetings, held along the East Coast, are regularly attended by 75 to 125 members, including one who flies in every month from Madrid. One Sunday every month, 30 to 40 members gather for emotional support meetings led by a organization-hired therapist.

''That's become a very important part of the (healing) process and the organization,'' Ammerman said.

On the 21st of each month, members hold a vigil outside the Pan Am Building in Manhattan.

Thursday, the one-year anniversary of the disaster, the Saunderses will be among scores participating in a candlelight march to the Pan Am Building. There, they will read aloud the names of the 270 victims. At Holy Trinity Church, Washington, D.C., an ecumenical service will commence at 2:03 p.m., the moment the ''Clipper Maid of the Seas'' broke apart in a fireball, the result of plastic explosives.

But Victims of Pan Am Flight 103 has a dark side. People unaccustomed to the international stage were thrust into news conferences, television appearances and congressional meetings. As egos swelled, an internal power struggle unfolded.

Disgusted, Saunders withdrew from September board elections, although his high profile assured his success.

''I didn't need to be in the limelight all the time. But it was damn important to some of these other people,'' Saunders said from his Clinton, N.J., home. * * *

Two days before last Christmas, Saunders stood in the Episcopal Church of the Mediator in west Allentown and eulogized his son.

''There's an empty feeling that I know will never go away,'' Saunders told more than 520 mourners that day. ''The irony of all this in my mind is Scott is now at peace, but those he leaves behind will suffer greatly.''

In January, Saunders flew to London. At Maria Assumpta educational center, home to Colgate's history study group, he met with the Catholic school's nuns. In the gardens, he planted a Bay tree bearing a memorial plaque to Scott.

At Lockerbie, Saunders saw the crash crater he had seen in news photos, but, somehow in person, it was different.

''It was more awful than words can describe,'' Saunders said in a soft voice that occasionally trembled with sadness.

As the year passed, Scottish authorities returned Scott's personal belongings after meticulously identifying and examining each item recovered at the crash site for bombing clues.

Clothing arrived first, followed by his passport, driver's license, personal documents and, two weeks ago, his photos of England and Spain.

Scott's resume, ''which fell 31,000 feet,'' is specked with mud and dirt, Saunders said. But Saunders is clearly moved the most by a loden green, three- quarter-length English jacket that Scott intended to give him for Christmas. It hangs in Saunders' closet.

''It just tears you up,'' he said. ''The pain is searing.''

After his retirement, Saunders said he will volunteer to speak to any group about airport and airline security and terrorism. He also plans to spend more time with Scott's brother, Greg, 19, who transferred from Hobart College in Geneva, N.Y., to Lehigh University in part to be closer to home after the tragedy.

''You never expect to lose a kid at 21. There's always time. Well, there isn't always time,'' Saunders said.

Lindsay and Greg's mourning has been more private.

Lindsay goes to local meetings of Compassionate Friends, an international group for parents who have lost children. She said her weekend real estate work precludes attending Victims of Pan Am Flight 103 meetings.

Linsday keeps the condolence cards the family received in the old stone farmhouse she and Greg call home. The cards and an occasional song on the radio are bittersweet reminders of Scott.

''Last year at this time there was the excitement of him coming home. But he'll never be coming home,'' Lindsay said. ''You know there is that song, 'I'll Be Home for Christmas.' And it's sad.''

Greg, a sophomore business major, said he keeps busy at Lehigh to block thoughts of his brother. He accepted Scott's diploma last May at the Colgate University commencement. But he said, ''I should have been in the crowd watching him accept it. It was really tough to go up.''

Greg has attended Victims of Pan Am Flight 103 meetings in New York, New Jersey and Pennsylvania. He said was relieved by media reports linking the PFLP-GC and Iran to the bombing.

''It would be nice to see them brought to justice. But it doesn't mean a whole lot,'' Greg said.

Like Mack Saunders, Jane and Jack Schultz have grappled with losing their surviving son aboard flight 103 by becoming activists in Victims of Pan Am Flight 103.

The Ridgefield, Conn., couple were to go to Lockerbie for the one-year anniversary, but now plan to attend an inter-faith service at a local Catholic church.

Jane Schultz, an Allentown native, said the body of their son, Thomas, was returned to them on his 21st birthday, Jan. 5. An honors student at Ohio Wesleyan University, he died returning from a Syracuse University program in London.

Schultz and her husband, chief executive officer at B. Altman & Co., buried their son in Stamford, Conn., next to his younger brother, Andrew, killed in an explosion 11 years ago.

''People say to me, 'How do you get through each day?' And I say, 'Well, we looked on our children as gifts and unfortunately we had to give them back sooner than we would have liked. But we're richer for having them,' '' Schultz said.

Attending the University of Dayton from 1965 to 1969, the depth of the Vietnam War, Bert Ammerman was at odds with campus activists who called for America's withdrawal. But lobbying in Washington - a city he called ''a cesspool of unaccountability'' - has changed his view.

''This 10-month maze through the jungle of bureaucracy has given me greater respect for the activists,'' said Ammerman, describing himself as a Republican.

''I certainly have gained greater respect for Ralph Nader and Senator (William) Proxmire, who used to give out the Golden Fleece Award.''

Victims of Pan Am Flight 103 at first were stunned by Bush's initial refusal to appoint a presidential commission.

Now, after months of what Saunders called Washington's ''bland official posture,'' members are disillusioned by government refusal to divulge results of the international investigation or even acknowledge that PFLP-GC leader Ahmed Jibril and Iran are the prime suspects.

''Our government has really let us down during the last year,'' Schultz said.

Ammerman said the group's attitude is typified by member Wendy Geibler's statement: ''I lost not only my husband. I lost my country.''

Saunders said he is incensed that the United States released $700 million in Iranian assets and offered reparations for people killed when a U.S. warship mistakenly downed an Iranian Airbus in 1988.

The statements are almost jarring coming from this group of well- educated, affluent people. But Victims is adamant about its agenda. The group is pushing Congress to pass legislation early next year requiring the federal government to train, evaluate and monitor airport and airline security.

And, at least, Victims of Pan Am Flight 103 wants the United States to impose diplomatic and economic sanctions against nations harboring or sponsoring terrorists. The organization favors military strikes as a third option.

''They are committed to loved ones who lost their lives, which is a much higher commitment than a political commitment. A political commitment is to stay in power,'' Ammerman said.