First it was just the newspaper interviews and, the radio and television talk shows to contend with.

The some foreign governments called about getting his plans, and the FBI and CIA moved in.

Finally, Universal called about the film possibilities.

After that there was nothing for John Aristotle Phillips to do but get a lawyer, an agent and an answering service. His Princeton roommates were going crazy with all the calls.

At 21, Phillips was a star.

Most people at some time or other dream of making it to the big time and the big bucks - national celebrity through winning the lottery, the Irish Sweepstakes, promoting a backporch invention into the millions - but few ever do and no one thinks about the afteramth.

Phillips has been living with it for over a year now.

"Here I was just an obscure undergraduate," recalled the brown-haired, blue-eyed youth. "I am a strictly average student, in fact, sometimes below average, and suddenly, I was famous.

It all started out so simply, Phillips recalls. When he was a junior at Princeton majoring in physics, he decided to show how easily an A-bomb could be made with information readily available in public libraries. He proved it in a 34-page paper entitled "The Fundamentals of Atomic Bomb Design: An Assessment of the Problems and Possibilities Confronting a Terrorist Group or Non-Nuclear nation Attempting To Design a Crude Plutonium Fission Bomb." Though he didn't actually make a bomb, he demonstrated that it could be done and in the process pointed up the need for tighter security on information concerning nuclear technology.

The paper garnered him an A and also thrust him into the limelight, though, in fact, Phillips is not the first student to have designed an atom bomb. An MIT student designed one earlier for a Public Broadcasting Television show.

It was Phillips, however, who get the notoriety. While family and friends told him to relax and enjoy the fame ("They told me it probably wouldn't last more than two weeks") the interviews and articles continued to appear, the lastest being a mention in Time magazine this week.

The most bizarre aspect of his fame was being contacted by French and Pakistani callers who said they wanted to see his design plans. "Everybody said it would be worth my while," he recalls of the telephone conversations. Philips, however, was cautious. He contacted Sen. William Proxmire because "I respect his positions on things," and Proxmire put him in contact with U.S. security agants who handled the situation. Thye even traslated his mail from foreign admirers, one of which was "filled with flattery and a marriage proposal."

The exposure has cooled Phillips' ardor for fame. He "canned doing talk shows because they're no fun," and will not be giving interviews this summer because he's writting a book on growing up in the 1970s, and becoming famous. He plans also to touch on the importance of procting plutonium (a key ingredient in making an A-bomb) from terrorist groups.

He says he's learned how important his friends are because "accquaintances are always trying to get a little piece of you." He found himself "embarrassed" in front of 500,000 Canadian television viewers when a folk singer crooned a paean to him with the lyrics, "Would you buy a pizza from the boy who made the bomb?"

"It was terrible," recalls Phillips, who with his Princeton roomate, David Michaelis, once ran a pizza agency at school. "It was horrendous."

Among the other "horrendous" experiences, Phillips names the fan letters from "lots of girls with photographs and promises," the marriage proposal from a woman in Gabbon and seeing himself altered in foreign press articles.

"In the Japanese version of Playboy, they changed my picture so that I looked Japanese," he says. "In the Swedish story, they lightened my hair. I used to have a thin little mustache, and in an Italian newspaper article, they darkened it so that I looked like a gigolo. The passport people would go crazy trying to identify all these pictures as me. I dread opening up newspapers now."

There have been positive experiences. He was in town yesterday to become a member of the board of New Directions, a kind of Common Cause international organization that lists among its members anthropologist Margaret Mead, Secretary of State Cyrus Vance, John W. Gardner and Norman Cousins.

"Probably the most wonderful thing to happen to me," he says," is sharing a podium at the World Affairs Conference in Boulder with Buckminster Fuller. He sent me all his books afterward, which I thought was a nice touch."

Phillips also says he's enjoyed his fame because "Now I realize how worthless being famous is. I know there are people who are bound to say, 'Well, you've made it so why shouldn't you feel that way,' but otherwise I might have spent my entire life seeking just those things. Now, I very honestly want to make a contribution to mankind."

Phillips lives in North Haven, Conn., with his father, Aristotle Phillips, a Yale University engineer and applied science professor, his mother, Bessie, a younger brother, Dean, who is a freshman at MIT.

Though he won't disclose how much money he has, Phillips does have a famous New York literary agent, Sterling Lord, and has received an advance from the William Morrow publishing house.

Recently he got a patent for his motorcycle crash protective system and argues that if it " retails for $50 and there are 3 million motorcycles and I make $5 on each, that's a lot of money." He says Honda and Harley Davidson motorcycle companies are already interested.

When pressed about his finances, however, Phillips says, I've got enough to afford a lawyer."

While he waits for his invention to pay off, spends his summer writing a book, what Phillips is really hoping for is to be accepted as an astronaut by NASA next year.