Alexandria Commonwealth's Attorney William L. Cowhig overspent his salary by as much as $2,000 a month during the period when he allegedly received the same amount -- about $2,000 a month -- in bribes, a key prosecution witness testified yesterday.

The expenditures went primarily for a monthly mortgage payment of $1,820 on a hotel in the Bahamas owned by Cowhig and his mother and for an airplane Cowhig financed for several months, according to the witness, Coy Ivy, a Virginia State Police investigator.

The fourth day of the bribery trial -- unprecedented for an incumbent Virginia prosecutor -- was marked by angry shouting matches between attorneys, heated arguments at the bench concerning the admissibility of prosecution evidence, and pointed warnings by Judge Percy Thornton Jr. to defense attorneys to stop making "extraneous remarks" about witnesses and evidence.

Special prosecutor Edward J. White jumped up once to say he had been "slandered" by defense attorney Leonard B. Sussholz, who countered that "never in 30 years of practicing law" had he seen such unfair courtroom procedures as he claimed White had used. Defense attorney Louis Koutoulakos told the judge the case against his client "stinks."

Cowhig, meanwhile, listened from the defense table, drumming his fingers lightly on its surface and looking on impassively except for whispered exchanges with his lawyers.

Cowhig is accused of asking for and receiving $32,000 in bribes between Jan. 4, 1977, and May 1, 1978, from Dirgham Salahi, director of the Montessori School of Alexandria. Cowhig was indicted Aug. 3.

During his day-long testimony, Ivy said that an examination of Cowhig's records showed no expenditures for "food, laundry or general living expenses" for 12 of 16 months he allegedly was taking bribes, and that there were unexplained cash bank deposits of $7,750 during the same period.

Although Cowhig's records claimed net income each month during the period of the alleged bribes of $1,811, his expenditures often totaled as much as $3,817 each month, Ivy testified.

Sussholz vigorously attacked Ivy's testimony throughout the day, and protested in front of the jury that Ivy was biased against his client. Sussholz declined, however, to cross-examine Ivy.

White rested the prosecution's case against Cowhig after introducing the 1978 incorporation papers of an aviation club Cowhig formed in 1977 to sponsor bingo games.

Defense attorneys said in court they will ask on Monday for dismissal of the charges, and reserved the right to recall Ivy to the stand.

The Montessori bingo games run by Salahi were among the most lucrative in Alexandria, and grossed more than half a million dollars last year.

Salahi's testimony in Alexandria Circuit Court on Wednesday provided the only direct evidence against Cowhig, and was challenged by Koutoulakos in a strenuous cross-examination.

Salahi acknowledged on the witness stand that he had once lied in a police report relating to the alleged bribes. He also changed his testimony about the size of a cash loan he claimed he had received from an Egyptian friend, saying it was $15,000 and not $50,000 as he had previously stated.

Salahi was granted immunity from prosecution in exchange for his testimony.

"Something stinks in this case, I don't know what it is, but it stinks," Koutoulakos told Thornton yesterday after the jury had left the courtroom. "White has been taken in by this man [Salahi]... [who] destroyed records and tapes that would have cleared Cowhig."

Thornton denied several defense motions to declare a mistrial or dismiss the charges against Cowhig, the first commonwealth's attorney in the history of Virginia to be indicted while in office.

White told the jury in his opening argument on Wednesday that Cowhig's motive for taking bribes from Salahi was "money, which he needed badly." Ivy's testimony yesterday was intended to back up that contention.

Ivy, a certified public accountant who spent 25 years as an FBI agent before joining the Virginia State Police four years ago, testified that according to documents received from the city of Alexandria, Cowhig's takehome pay during the period of the indictment was $1,811.61 per month.

All of Cowhig's city salary checks were deposited in a checking account at the Burke and Herbert Bank in Alexandria, and a personal financial statement from this period filed by Cowhig stated that he had no sources of income except for his salary, Ivy testified.

But Ivy said no checks drawn on the Burke and Herbert checking account went to meet a monthly mortgage payment of $1,820 for the Two Turtles Club, in the Bahamas, which Cowhig owns, or to meet a monthly payment of $1,057.80 for an airplane Cowhig owned for four months in 1977.

Ivy testified that he had managed to account for several payments on the Two Turtles Club mortgage by means of a $2,500 cashier's check Cowhig purchased for cash, and other checks. including one drawn on Cowhig's account at the Bank of Nova Scotia, located in Georgetown, Exuma, the Bahamian island where the club is located.

Ivy testified that he had not been able to gain access to the records of the foreign bank, since Bahamian banking laws regarding privacy "are as strict as those in Switzerland."

According to the mortgage payment record from the Alexandria National Bank, which had lent Cowhig $150,000 for the purchase of the club in 1973, Cowhig made interest-only payments of $851.84 in January, February and March of 1977, Ivy testified. From April 1977 to April 1978, Cowhig successfully met the full interest and principal payment of $1,820 each month, Ivy said.