Shortly after federal prosecutors rested their case in the political corruption trial of Maryland Gov. Marvin Mandel today, codefendant Irvin Kovens, through his attorney, made the startling announcement that he would present a defense.

Norman Ramsey, attorney for Kovens, formally put to rest the case for Kovens immediately after U.S. District Judge Robert I. Taylor denied motions for acquittal of the co-defendants, including Kovens. Mandel's closest friend and financial benefactor.

"This is not pro forma," Ramsey said, "it is for real. If you deny the motion . . . we are prepared to rest our case and bring our case to an immediate end."

The other defendants will present witnesses in their own defense and most of them, including the governor, are expected to take the stand.

The jury will decide Kovens' guilt or innocence of political corruption charges on the 24 days to evidence completed this morning by the government and on the arguments presented by his codefendants over the next few weeks.

Experienced attorneys not involved in the case offered several possible explanations for Kovens' actions today. By resting his case, they said, Kovens might be attempting to improve his chances for appeal if convicted. In some circles of law, it is believed that any evidence produced after a defendant rests cannot be considered on appeal.

Or, the speculated. Kovens might have felt that by subjecting himself to cross-examination by the tenacious Assistant U.S. Attorney Barnet D. Skolnik, he could only lose ground.

For whatever reason, they all agreed that it was rare for one defendant to resist telling his side of the story while the others mounted their own arguments.

Throughout this trial, the second attempt to try the Mandel case, Kovens has been a consistent wild card.

He was absent because of ill health from last years' trial, which was aborted following two outside attempts to tamper with the jury. This time around, with Kovens as a defendant, the prosecution was able to present major new evidence of the alleged corrupt relationship that lasted from 1969 until 1975.

The government's 23-count indictment charging Mandel with defrauding the state by taking part in a financially enrivhing scheme with his five codefendants rests on two premises. Mandel received hundreds of thousands of dollars worth of gifts and favor from his friends as bribes according to testimony. For these gifts, Mandel allegedly lobbied for legislation that brought windfall profits to the Marlboro Race Track secretly owned by the codefendants.

The new evidence about Kovens - a major Baltimore political boss - added substantially to both sides of this alleged scheme at the retrial. The list of gifts at the last trial added up to some $200,000. With Kovens, the wealthiest defendant by far, the figure shot to $350,000.

The importance of Mandel's alleged lobbying efforts also became more significant because Kovens, was said to hold 60 per cent of the stock of the race track.

Four other codefendants, W. Dale Hess, Harry W. Rodgers III, William A. Rodgers and Ernest N. Cory Jr., together held only 35.56 per cent of the stock.

Prosecutors presented several important pieces of evidence, including Kovens' gifts to Mandel, two laundered loans to the governor and Kovens' alleged 60 per cent interest in the track.

Yet it was a streamlined presentation, eight days shorter than the first prosecution case. The testimony of about 20 people who were witnesses in the first trial was read and agreed to by both sides, substantially cutting down on arguments among the lawyers.

This time has been saved despite the abbreviated trial schedule adopted for the sake of Mandel's own failing health. Shortly before the retrial, the governor suffered what doctors believe was a minor stroke and his attorney won what was to have been a relaxed work week of three full and two half-days.

But under Judge Taylor's strict stewardship, more testimony has been packed into each day of these proceedings than at the previous trial. Taylor says he keeps up a demanding pace in order to lessen the days that the jury must remain sequestered.

At the trial, the jury was allowed to go home each evening but since the mistrial was declared over publicized accounts of the verdict tampering attempt, this jury must live under strict surveillance at a suburban Baltimore motel.

Mandel's divorce, almost incidental in the last trial, became a centerpiece of the prosecution's charge that Mandel was "bought," through bribes, by his codefendant.

Kovens gave $155,000 worth of bonds to Mandel's former wife Barbara on the day in 1973 she finally agreed to leave the governor, and he allegedly personally guaranteed Mandel's payment of the private settlement, estimated at $400,000.

When it came time for Mandel to meet his first lump sum payment required by the settlement, he turned to Hess and Harry Rodgers for help, according to testimony and evidence.

They arranged a laundered loan of $42,000 through the Pallottine Father's Catholic order to meet the 1974 $369.062 payment, according to new evidence in this trial.

Later, according to testimony, another loan of $12,000 from the Pallottines was laundered through several layers to conceal its origins and given to the governor's new wife, Jeanne Mandel, who had not been mentioned as a recipient of favors in the last trial.

The evidence that marked Kovens as the majority stockholder in the track was unveiled this week. Prosecutors did it by connecting a code name "Zar" to a secret list of stockholders, a phone number on the back of a business card and a page from the Baltimore telephone directory.

Kovens, however, is not alleged to be part of the two major ventures cited in the three anti-racketerring counts in the indictment.The prosecution alleges that Mandel was given an interest in an Eastern Shore real estate venture worth some $47,400 by Hess and the Rodgers brothers.

The prosecution also alleges that Mandel was given four-ninths of Hess' interest in an office building owned by Hess and the Rodgers brother that was estimated to be worth some $138,000.

While these gifts were described as neccessities for Mandel's well-being, the others fall into the category of luxuries.

The defendants gave Mandel some $4,800 in Florida vacation trips, a new, stylish wardrobe worth 3,642, diamond jewelry valued at $7,816 and help in meeting an insurance premium payment that was part of his divorce settlement, according to testimony.

The defendants are expected to take the general posture that the gifts and favors were expressions of friendship. However, William Rodgers and Cory will try to sever themselves from the very close relationship enjoyed by Mandel, Hess, Harry Rodgers and Kovens over the past 15 years.

No one has testified that Mandel knew about his friend's secret purchase of the race track on New Year's Eve, 1971. The prosecutors are expected to rely in part on the very close friendship of the defendants when arguing that there is no way that he could have not been aware of the purchase.

Mandel vetoed a bill in May of 1971 that would have doubled the racing days, and vastly increased the profits, of the Marlboro Race Track. Seven months later his friends secretly purchased the track.

When the veto was overridden in January, 1972, legislators testified for the government that Mandel acquiesced in an override vote. One state senator testified that Mandel's chief senator testified that Mandel's chief legislative lieutenant actually said that the governor wanted the override.

In that same session a racing bill was introduced that, among other things, would have added another 58 racing days for Marlboro. Since one of the aims of the bill was the elimination of half-mile tracks like Marlboro. legislators took out that section of the bill.

Testimony from legislators - most of whom were avowed Mandel opponents - had Mandel lobbying the bill through his aides and allies and also put him in a last-minute vote counting session with Hess the night before a crucial vote.

Because of a threatened filibuster the bill failed. Two years later, however, Marlboro won approval of a merger of racing days with Bowie and stocks in the track became even more valuable.