Maryland State Sen. Julian L. Lapides testified today that he switched his vote in 1972 because "it was my belief that the governor wanted his veto overriden" on a bill that benefited the Marlboro Race Track.

An avowed opponent of Maryland Gov. Marvin Mandel, Sen. Lapides explained at the Mandel political corruption trial how the governor's lobbyists were clustered in small groups around the Senate lounge that day but they were not asking the senators to "sustain the governor's veto."

The veto was overriden, without Lapides' vote, and the bill became law allowing the race track to double its racing days and bringing benefits to Mandel's friends and codefendants who secretly owned the track.

That veto override and the actions of the governor and his allies in promoting a race track consolidation bill the same session are key to the prosecution's case against Mandel and Five codefendants.

Codefendants W. Dale Hess, Harry W. Rodgers, William A. Rodgers, Ernest M. Cory Jr. and, allegedly, Irvin Kovens secretly purchase the track on Dec. 31, 1971. The prosecution alleges that these men gave Mandel some $350,000 worth of gifts in return for which Mandel lobbied for the legislation in 1972.

Earlier, Sen. Victor L. Crawford testified that there were rumors circulating that "Hess, Rodgers and Kovens" owned the track but it was never proven.

Crawford said that if he had known that to be the case it would have relevant to his deliberations on the veto override and the bill because "it meant windfall profits to close personal friends of the governor . . . and would have had the appearance of wrong-doing."