YOUTH GETS NEW LIFE AFTER SUICIDE THREAT

By WILLIAM K. STEVENS, Special to the New York Times

EVERMAN, Tex., April 22— The streetwise manner, a certain edge to the personality that comes from having had to endure too much too soon, is there. Otherwise, surrounded now by the family he never knew, Michael Buchanan, in his cowboy boots and peach-colored Western shirt, could have been any other 18-year-old in this prairie suburb just south of Fort Worth as he fixed that staple of teen-age life everywhere: a bologna sandwich.

Last September, Michael found himself on the roof of a flophouse in New York's Bowery. Jobless, penniless, filthy, sick, starving and crushingly alone, he was about to hurl himself to the street.

''Jump! Jump!'' cried the crowd below. William Fox, a New York City policeman routinely assigned to such cases, talked him out of it. And, in an act that led to a flood of recognition and applause, he took Michael into his home on Staten Island and became the legal guardian of a runaway whose father had abused him and whose mother was presumed dead. It seemed a happy ending to a potentially tragic story.

But now another chapter has begun. It is part of a story that could have come straight out of Dickens, or, with many variations both grim and happy, out of the experience of thousands of modern youths in an America whose mobility and loosening family structures help set them adrift in the world. 16 Years of Separation

All these years, Gloria Hunsinger had known nothing of the son whose custody she relinquished 16 years ago in the divorce settlement that ended a brief and disastrous teen-age marriage. Once she heard that Michael had been killed in a motorcycle accident. She never knew for sure what had become of him, however, until a Fort Worth newspaper printed the story of his rescue and adoption in New York.

One thing led to another, and Michael Buchanan, by his own choice, has come home at last. After a youth spent largely in neglect, in foster homes or on the run, he has come to rest in a warm setting with his hard-working mother and stepfather, a long-lost younger brother, a stepbrother and three dogs, including an English setter named Jenny that sleeps on the bed.

''I had love in both places,'' Michael says in trying, with some apparent difficulty, to explain why he left the person who saved his life in New York. ''It's just that I felt that this was my home.''

''You're talking about a boy who never had that in his entire life,'' Officer Fox said in a telephone conversation from the base of Emergency Unit One on East 21st Street in Manhattan. Officer Disappointed at First

The officer, who adopted Michael, gave him a home for seven months andset up a trust fund for his education, minimizes the disappointment he felt over the youth's decision. But according to Michael, there was some unpleasantness at first.

''We had a couple of arguments,'' Michael said as he attacked the bologna sandwich. ''He hung up on me and I hung up on him.'' The policeman and his ward talked frequently on the telephone when Michael came to visit his family in Everman for the first time. Michael would call, brimming with excitement over what he had found here.

''We had a good feeling he was going to stay,'' the officer says. But when Michael finally made the critical decision, he couldn't bear to break the news. He put off calling Officer Fox until two days after he was supposed to have returned to New York.

''I just didn't want to tell him,'' says Michael. That, he says, is basically what caused them to quarrel. But in a couple of days, Officer Fox called and said that if Michael was happy, he would be happy. Now, he says, he sees that Michael's living with his natural family ''was something he always wanted and never had.''

''I could never replace that,'' said Officer Fox. ''Nobody could. It made me feel good that he had found what he was looking for and that I was instrumental in helping him out.'' Son Was Taken From Father

When Mrs. Hunsinger and Michael's father were divorced here and the father gained custody of 2-year-old Michael, the mother gained custody of a second son, Jimmy, now 16. Michael and his father moved to Memphis, and only recently did Mrs. Hunsinger learn, from official records, that Michael was taken away from his father after reports of abuse and desertion. Once, she said, the father left Michael alone in a locked automobile for eight hours. He was subsequently sent to live in a succession of foster homes, first in Memphis and then in Morganton, N.C.

In Morganton last year, Michael developed what seems to have been a romantic yen to see New York City. ''I guess I dreamt of New York as a little bit of Hollywood,'' he said, ''imagining all kinds of famous things. But it's like any place else, a crummy city with lots of people.''

The romantic dream turned to a nightmare within a week after Michael arrived in Manhattan with $7. One thinks of Oliver Twist in London.

He says he spent his time in those grim early days ''mostly walking around looking for a job and a place where I could sleep.'' He found only one brief job, cleaning store windows on Canal Street. Finally, exhausted, hungry, having had no bath or change of clothes in two weeks, he ended up on the Bowery roof.

''Nobody cares,'' a tearful Michael told Officer Fox when the policeman tried to talk him down. The officer succeeded by offering him the spare room in his home on Staten Island. Security on Staten Island

Michael then enrolled in Curtis High School, joined the chorus and began living a secure life. Mrs. Hunsinger learned of all this when her mother in Fort Worth read about it in the newspaper and telephoned Officer Fox.

All this time, Michael was under the impression that he had been abandoned by his mother. When she tried to telephone him on his 18th birthday, March 29, and explain what had really happened, he didn't want to hear about it. But he relented, called his mother and told her he wanted to visit her over Easter vacation.

''I just decided to spend Easter with her,'' he said. ''I wasn't planning on staying at first.'' Today, Michael and his brother have struck up a friendship. They go camping and fishing together. Their conversation is punctuated with mild insults, as was the talk between Michael and Officer Fox. The brothers sometimes go to Dalton's, a club for teen-agers that features both rock-and-roll and country music.

Sometimes they quarrel, as brothers will, but not seriously. Sometimes Mrs. Hunsinger quarrels with Michael, too, mostly over keeping his things picked up. She says he eats and eats and eats. Outlook for Graduation

Michael now lives on a quiet street of small, well-tended, ranchstyle houses just off a freeway. He has enrolled at Everman Senior High School, where he is taking advanced biology, honors algebra, American history and chorus. If the credits from his three previous schools can be transferred in time, he may graduate this year; if not, he will next year.

The future? ''I don't know,'' he says. ''I would like to get a college education because I think it's really important.'' But he says he is also thinking seriously about military service.

To Douglas Hunsinger, his stepfather, a glazier who works on highrise office buildings in Fort Worth, Michael seems a well-educated youth, mature beyond his years. As Officer Fox puts it, ''Mike's been out and around and knows what it's like out there.''

''He's had a lot of bad experiences,'' said his mother, who works in a school cafeteria and at night in a plastics factory. She notes that ''sometimes, child abuse leaves emotional scars,'' but adds that there is no sign of that so far.

''He seems to be just fine here,'' she said.