Just over two weeks ago, Tom Wager, 16, was planning a trip with his family to their lakefront vacation home near Charlottesville for the Memorial Day weekend. He was looking forward to going water-skiing.

On the afternoon of May 22, the day before the trip was to have begun, he went shopping with his mother and bought a squirt gun and balloons he planned to fill with water. He told her they were pranks for the last day of school, still two weeks away.

The next day, he went home after school and killed himself with his father's rifle. His death was ruled a suicide.

He left behind no note, no diary, no overt indications that he was deeply troubled, although there had been some seemingly minor changes in his behavior, according to accounts by his family and friends.

The suicide has come as an incomprehensible shock to those who knew Wager, because the blond, blue-eyed 10th grader at Bethesda's Walt Whitman High School appeared to have it all, his friends said.

He was a Boy Scout troop leader, a B-average student who was enrolled in an honors English class, and he played the saxophone in the school's marching and jazz bands. He had a summer job lined up restoring cars, one of his favorite hobbies.

And he drove a blue MG convertible, was popular in school and always smiled and cracked jokes.

"If I thought someone would kill himself, it would never have been Tom," said Francesca Fitchette, 15, a 10th grader at Walt Whitman who had known Wager since elementary school.

But in an era of rising pressures on teen-agers, Wager's suicide is not an isolated incident. Cases of teen-age suicides in Plano, Tex., and in Omaha in particular have focused attention on the problem. According to national statistics, the number of suicides among teen-agers has tripled since 1960 to more than 5,000 a year.

And the phenomenon has struck this area, where authorities have reported a frightening increase in the number of teen-agers trying to kill themselves.

Although the increase is puzzling, experts say that a suicide attempt can be triggered by stress over a broken romance, a bad grade, a family move, a death in the family, pressure to achieve, divorce or other events.

"Adolescence is a time of greatest grieving," said the Rev. William Wendt, an Episcopal priest who is founder of the St. Francis Center in the District, a nonprofit center that does research, counseling and education programs on death and dying.

"There are so many losses and so many mini-death experiences," he said. "There is the loss of childhood, the loss of innocence, the loss of a sense of a benign world.

"There is the loss of a girlfriend, a poor grade, a sense of failure. Then if you are also dealing with the death of a friend or a parent or grandparent or divorce then you are dealing with a lot of whammies."

The national nightmare was played out on a very personal level for Wager's friends and family last week as they tried to cope with his suicide and sought to find a reason for his despair.

About 200 friends and relatives gathered Tuesday in a church less than a mile away from Wager's school for a muted but emotional afternoon memorial service filled with poetry and music.

Scoutmaster Jerry Sullivan said Wager had been an ideal role model for younger scouts. Classmates Greg Maring and Alex Saenger said Wager had been a good friend. Wager's brother, Jeff, 18, said Tom had been "a great brother. Unfortunately, there was a part of him none of us ever saw."

Afterward, they sought to console each other, but the question of "Why?" haunted the group. Many parents were quick to blame the intense pressure for high grades and honors and for peer acceptance at Walt Whitman, an outstanding academic high school that serves students living in some of Montgomery County's most affluent areas.

"There is so much pressure on all of us, even if we don't show it," said Lizzie Trinidad, 16, a 10th-grade honors student and friend of Wager's. Others pointed to the growing disenchantment among some students with being unable to meet the goals or standards they or their parents set, a disenchantment that leads some students to drugs, alcohol or crime and may lead others to suicide.

There were no easy answers. Wager's parents say they are still searching for clues.

"There were no indications," said his father, Joseph Wager, a lawyer. "There were no changes in personality. There was no depression, no moodiness."

"I cannot in my wildest imagination credit him with being such a consummate actor as to have contemplated this beforehand," said his mother, Peggy.

Many teen-agers do contemplate suicide. Some, like Wager, carry it out.

In Maryland, there were 104 teen-age suicides in 1984, up 300 percent since 1957, according to the Maryland Chapter of the National Committee for Youth Suicide Prevention. In Virginia, 112 persons between the ages of 15 and 24 committed suicide in 1984, officials said.

In the years 1981 through 1984, according to police department statistics, 214 Montgomery County teen-agers attempted suicide and nine succeeded.

Fairfax County officials, alarmed by a growing number of teen-age suicides, began a program for teachers alerting them to the early signs of suicide that has been credited with reducing the number there from 20 in the 1980-81 school year to three in 1982-83.

Ed Masood, director of health for the Montgomery County public school system, cautioned that Montgomery's figures may actually be higher because many teen-age suicides are reported as accidents.

Concern about the problem this year prompted the Maryland General Assembly to adopt a bill mandating that all public school systems offer suicide prevention education. Six school districts, including Montgomery, will put pilot programs in place by fall to teach students how to deal with pressure.

In Montgomery, a suicide prevention task force has been studying the problem and will recommend to the school board what kinds of prevention programs should be established.

Although many suicide victims appear depressed, moody and lethargic before taking their lives, some display few outward signs that they are troubled, experts say.

"It's not at all unusual for a lot of young people who appear happy and well adjusted and forward looking" to commit suicide, said Penny Finch, a school psychologist in Montgomery County who last week held a counseling session for about 150 students who knew Wager.

"That's because inside they've made a determination to solve their problems" by killing themselves, she added.

"There are signs," Masood said. "To someone untrained to recognizing those signs they mean nothing. To someone who is trained they mean a lot."

Always a good student who stayed out of trouble, Wager in recent weeks had started displaying discipline problems, one of the warning signs of someone who may be having trouble coping, experts said.

He and a friend had thrown eggs at his band teacher's house. As punishment, his parents told him that he could not drive the MG for two months and had to be in by 9 p.m.

The afternoon he shot himself, he skipped his last-period band class and was drag-racing in the school's parking lot, friends said.

An assistant principal told Wager he would have to serve three hours of detention after school as punishment.

"He was not upset," said Greg Maring, 16, a 10th grader and Wager's best friend. "He almost thought it was funny."

There also was another sign that could be related to the suicide, friends said.

Two weeks before Maring's birthday, Wager gave Maring a birthday present. It was a disk with a picture of the rock group The Police, one of Wager's favorite possessions. Another sign that someone is contemplating suicide is when the person starts to give away possessions, according to the experts.

During a recent band trip to Ontario, Wager's father said, Wager and a friend were at the top of a tall building when the friend commented on the danger of falling from that height. "I really wouldn't care if I was alive or dead," Wager responded to his friend, according to his father.

Last week, Peggy Wager went to the high school to clean out her son's locker. She went through his notebooks and papers searching for a clue.

All she found were a poem and a short story on death that he had been studying in one of his classes, hardly the kind of evidence she was looking for.

"I know there are answers," she said, "but we are never going to know what they are."