Thomas C. Nibali was acquitted of bribery charges for the third time in seven years last week but he still feels far too embarassed and angry to talk about it.

He won $200,000 in back-pay and was reinstated in his old job as an Internal Revenue Service supervisor as a result of last week's court action. But that came seven year's after he was acquitted by two juries of all charges and maybe that is the reason, he says, why accepting the victory is not easy.

"You can't live seven years all over again. My family can't and the $200,000 can't," said Nibali, now a 55-year-old attorney for the Maryland public defender's office.

His union is jubilant about the decision, reached by a United States Court of Claims judge last week and made public yesterday. The National Treasury Employes Union sent out a press release, union official Jerry D. Klepner calling it was an important decision."It's a big case, the sheer amount of money involved. It's the most I've ever seen and I've been around for seven years," he said.

Nibali was surprised about the press release and a reporter's phone call. "I didn't know, I didn't think would ever be asked that's bothering me," he said.

The questions began in 1968 when an accountant told another IRS agent that two of his clients were planning to pay a $15,000 bribe to Nibali to avoid higher income tax payments. By 1971 that had turned into an indictment.

At his first trial by jury that May, Nibali was acquitted of all but one charge. The jury was hung on that point, so another indictment was issued and Nibali brought to trial before a jury in December 1971. This time he was acquitted on all accounts and for five days life again was normal. Then the IRS fired him, citing as its reason the exact charges on which he had just been acquitted: "soliciting and accepting a $15,000 bribe."

"I just don't talk about this, about my past life with most people. It's just a hurt," Nibali explained.

Money, of course, was the first problem he faced. And then there was the fear that the accusations would harm the projects on which hwas working at his church, St. Anthony's parish in Baltimore. The "hurt" done to his wife and three children as a result of the accusations did not need to be explained he said.

That first year he earned $2,000. Since his old salary in 1970 had been $23,000, he had to dip into savings to meet mortgage payments. His wife got a job and eventually he was able to get one, too.

In the spring of 1972 the Maryland public defender's office hired him on as a clerk accountant (he is an attorney besides being a 23-year veteran IRS agent). In three years he was promoted to full-time public defender, trying criminal cases by day while he worked on his own appeal during the evenings.

"I was 49 years old when this happened," Nibali said. "I'm sure most of my friends believed I was innocent but you still had that hanging over your head, not knowing what would happen. You try to hide the fact from yourself that it's happening to you.

His initial legal fees of $10,000 have yet to be paid. His union has mounted the last six years of his defense. His income dropped to $14,000 a year until 1975 when he began earning the $19,000 salary he has today. In addition, each tax season he would moonlight preparing tax returns.

His eldest child is a 31-year-old daughter and he has two sons; 28- and 18-years-old. All three, he said, "had it hard. It hasn't been pleasant for them, the questions they've had to answer.

"The average person could never have borne all of this. Just those finances, it's prohibitive to fight and appeal without a union or something behind you," he said.

The victory he has yet to accept, he repeated. "I haven't made any decisions about going back (to the I.R.S.) . . . It (the IRS firing) was something that constantly preyed on my mind. You just can't shunt that aside."