A Presidential Salute to One of New York's Finest

By Albin Krebs and Robert McG. Thomas Jr.

A New York City police officer who persuaded a distraught youth not to fling himself from a Bowery flophouse roof, then later took the youth into his home, has received a written pat on the back from President Reagan.

In the letter to William Fox, a 35-year-old bachelor who lives on Staten Island, Mr. Reagan said: ''How inspiring to read about your humanity and determination to save a young man filled with despair.

Nancy and I want to tell you of our deep admiration for your act of steadfastness to save Michael.''

Last month Mr. Fox served as part of a team sent to get Michael Buchanan, a homeless 17-year-old, down from the roof, while people of the street below shouted ''jump, jump.'' Mr. Fox told the youth that suicide was not the way out and that ''somebody cares.''

Since then Mr. Fox has taken Mr. Buchanan into his home and this week Family Court gave him legal temporary custody of the youth. A ruling on permanent custody is expected next month.

The Patrolmen's Benevolent Association said yesterday that an education trust for Mr. Buchanan had been set up with the aid of contributions from all over the country.