Former Alexandria prosecutor William L. Cowhig, confidently predicting that his legal difficulties are ended said yesterday he is "tearing at the bit ... ready to go" for a reelection bid.

"There is not a single reason why I shouldn't have my job back," said the 53-year-old Cowhig, who added that a final decision on whether to seek his old job had not yet been made.

"I haven't cleared it with my mother yet," he said with a smile in his new office across from Alexandria City Hall. "If she says no, then it's no."

Cowhig was indicted in August on three felony counts growing out of an investigation of alleged abuses in bingo games in Northern Virginia. He later was acquitted of two counts in jury trials, and quit his job as prosecutor in exchange for having the third charge dropped.

Cowhig still is the subject of at least two investigations, one by special prosecutor Claude Hilton, who is looking into allegations of sexual misconductedbo Cowhig while he was in office, and another by U.S. attorneys in Alexandria who are probing possible political corruption connected to the city's massage parlors.

Cowhig said yesterday he also has been "informally notified" of an inquiry by the Alexandria Bar Association into his possible disbarment. Alexandria lawyer Philip J. Hirshkop, chairman of the state bar grievance committee, refused to confirm or deny that such a probe is under way.

Hilton said "no decision has been made yet" on whether to seek Cowhig's indictment in connection with the alleged sexual misconduct.

Cowhig yesterday said he was confident he would be exonerated. "I don't want to second-guess Claude, but there was no crime, no [sexual] solicitation," he said.

Cowhig yesterday confirmed that he has circulated two petitions recently seeking pledges of support for a possible bid to regain the office he vacated las month.

He expects to gather 2,000 to 3,000 signatures of endorsement, Cowhig said, but would not formally file as a candidate in the upcoming Democratic primary until April 10, three days before the filing deadline.

Some local politicians and attorneys yesterday expressed dismay at Cowhig's statements.

I'm really surprised that he would do this after all he's been through," said Council member Arnold C. Casey.

Democratic mayoral candidate Charles E. Beatley said, "You have to have the trust of people [for commonwealth's attorney], Cowhig doesn't qualify on that basis."

Cowhig responded by lashing out against Beatley, Casey (a vocal Cowhig critic), and Cowhig's successor, John E. Kloch, who is running for reelection as chief prosecutor.

Cowhig called Kloch's recent request for a reduction in the prosecutor's $42,500-a-year salary, "bureaucratic garbage."

He (Kloch) put a figure on his own worth," said Cowhig. "He obviously thinks I'm worth more than he is."

Cowhig said his campaign would be managed by his longtime administrative aide, Mary Ann (Sam) Pastorek, who left her job with the Commonwealth's Attorney's office when Cowhig resigned. Pastorek, regarded as a SaVVy Alexandria political figure, is currently Cowhig's secretary in his new law office.

Special prosecutor Hilton said he has interviewed almost 40 people in his probe of the allegations of sexual misconduct by Cowhig. "I still have three or four people to talk to who might be able to shed some light on this thing," he said.

The investigation is focused on whether Cowhig solicited and received a sexual favor from the wife of a drug defendant in 1975. A senior Alexandria police offical recently resigned, admitting he has suppressed results of a police polygraph test allegedly implicating Cowhig.

In the U.S. probe, prosecutors said they are specifically interested in why massage parlors were able to flourish in Alexandria after being shut down in Arlington and Fairfax. "The investigation is not concluded," U.S. Attorney William B. Cummings said yesterday.

Cowhig was elected Commonwealth's Attorney in 1974, defeating incumbent John E. Keenahan. He was unopposed for reelection in 1978. In November, a candidate will be elected to fill the remainder of Cowhig's term, which expires in December 1981.

"A lot of people feel it's in my best interest not to run," Cowhig said yesterday. "But that office has been my entire life."