AS the perennially popular quiz show ''Jeopardy!'' would put it:

Question: Winner of $26,300 in the recent Teen Tournament.

Answer: Who is Sahir Islam?

Sahir, 17, a senior at Somers High School here with a perfect 1,600 SAT score, won the teen-age championship by answering questions at breakneck speed in categories from the Constitution to People Eat That? and besting 14 other teen-agers.

''I had watched the show for a couple of years,'' Sahir said. ''Then last year I became obsessed with it. My mom nagged me to enter, but I kept saying no. I guess I was scared.''

In June, Sahir finally agreed to enter and sent in a postcard with his name, address, age and high school. He was among the 1,500 randomly chosen to be tested for the competition. Tryouts took place in Philadelphia in August and they may have been the most stressful part of the tournament.

Sahir's mother, Sultana Islam, recalled: ''Traffic was awful, and the drive took six hours. We arrived late, and the testing had already started. Sahir was embarrassed and didn't want to go in, but I insisted. They were very nice and let him have extra time at the end.'' Mrs. Islam had watched ''Jeopardy!'' with her family and observed that Sahir ''got all the answers right.''

Test takers are allowed 15 minutes to answer 50 questions in 50 categories. To qualify, participants had to answer 35 questions correctly. Sahir was one of 12 of 100 taking the test in Philadelphia who passed. At about the same time, tryouts were held in five other cities.

''After the test, you play a mock game to test your reflexes on the buzzer and to make sure your personality isn't too boring,'' Sahir said. ''Three people were taking notes in front of us, and I think some more were behind us. I tried not to pay attention to them.''

Sahir worried because another contestant kept beating him to the buzzer, and he thought that his answer to the question ''What would you do with the 'Jeopardy!' money?'' was dull. He had said, ''Invest to pay for college.''

He tried not to think about the program for the rest of the summer, but he studied reruns. ''You can get a feel for the questions,'' he said. ''If you know how the writers think, you can answer the questions without knowing much about the category.''

For example, he guessed which flower Anders Dahl introduced by glancing at the botanist's name. Answer: the dahlia.

In September, Sahir heard that he had qualified for the first round. He masked his excitement. ''I told only one person, but he told the entire state of New York. My friends were pretty happy for me, and one offered to be my agent for 10 percent.''

Sahir's classmates helped sharpen his skills. ''We played Trivial Pursuit all the time -- in the lunchroom, in classes, everywhere,'' Elizabeth Marcantonio said. Another classmate, Sara Vitolo, recalled, ''At one party, it was everyone against Sahir, and he won.'' Sahir also won the first official round, taped in Los Angeles between Oct. 4 and 6. He went with his parents and stayed at the Beverly Hilton Hotel. ''Jeopardy!'' pays for the contestant and one parent. He brought back hotel shampoo, shower caps and sewing kits for his friends but could not tell them the outcome because all contestants sign nondisclosure agreements.

Sahir did disclose that Alex Trebek rests and sometimes drinks water during commercial breaks, that ringing in early locks a contestant out of answering and that the stage floor looks slippery but is not.

On Oct. 29 Sahir, his parents, who are from Bangladesh; his sister, Runa, 19, a Harvard student, and 10 other family members flew to Washington for the semifinal tapings. He beat two seniors from private schools by coming up with diverse answers like Howard Stern, John Hancock and Chaucer.

Sahir won the final rounds from Enos Williams and Kristen Stuckey, both from Texas, out-wagering and correctly answering the final question, which was about Kwanzaa.

Between rounds, the contestants visited national monuments and had a private White House tour, although they did not meet President Clinton.

It was the first time the Teen Tournament, which began in 1987, had traveled outside Los Angeles. ''We're going to do it again; it was so successful,'' Laine Sutten, a ''Jeopardy!'' spokeswoman, said, adding that the students are always more compatriots than competitors. ''There's such a bond between them. They have so much in common.''

Sahir agreed. ''It was probably the most fun I had had in a while. The best parts were before and after, meeting the people and the whole aura. Everyone was nice. If any one of them had gone to my school, I'd be friends with them.''

Meanwhile, Sahir kept his secret from his friends despite constant prodding. ''I thought he'd win,'' Henry Su said. ''I've known him since third grade. He was pretty up there even then.''

Watching himself on television was strange. ''You notice things like facial expressions, quirks that you never noticed before,'' Sahir said.

Finally, six weeks after his first ''Jeopardy!'' appearance, Sahir was a public hero, and eligible to play in the $100,000 Tournament of Champions, which will be held next year. A schoolmate asked for an autograph and Sahir wrote, ''Who is Sahir?''

Sahir, who heads his school's Academic Challenge team, plays drums in the jazz ensemble and marching band and has applied early to Harvard, plans to work on other college applications now.

But the thrill of college admission may not equal his victory on ''Jeopardy!'' ''There's a saying, he said, laughing. 'You're nothing in America, unless you're on TV.' ''

Photo: Sahir Islam, front, and friends watch ''Jeopardy!'' at his home in Somers. (Susan Harris for The New York Times)