Jean-Jacques Gunning seemed to have everything going for him. He was a respected doctor, successful hospital administrator, tireless contributor to charitible causes and a family man with a wife and three children.

There was only one hitch, prosecutors said in federal court today: He didn't file any income tax returns for 15 years, from 1965 to 1980.

Gunning, 53, medical director of St. Agnes Hospital here, acknowledged the accusation before U.S. District Court Judge Norman P. Ramsey.

He was sentenced to four years' probation, a $10,000 fine and 960 hours of community service.

Holding back tears, Gunning told the judge, "What I did was not justifiable, and I freely admit that."

Defense attorney Allen L. Schwait said that while there was no excuse, there was a reason for Gunning's failure to file the returns. "He was enormously busy," Schwait said, "and he began to procrastinate. After a year or two, fear took over and then paralysis."

No one has figured out exactly how much Gunning still owes in back taxes. As a Navy doctor and later medical director at St. Agnes, a large portion of taxes was automatically withheld from his salary, prosecutors said, but since he filed no returns, taxes from other income, such as interest, capital gains and his Navy pension, have not been entirely accounted for.

Prosecutors estimated Gunning earned a total of $106,908 in 1979 and $135,637 in 1980, for example, and owes $25,376 in additional taxes.

Schwait said all back taxes since 1975 have now been paid, but no determination has been made on taxes for the years before that.

Schwait described Gunning as a selfless "good citizen of the world" who over the years did relief work in Mexico, raised funds for lepers in the Philippines and assisted an orphanage in Vietnam.