The body of Richard J. Niederrriter, a 58-year-old Marriott Corp. vice president, was found in the Tidal Basin yesterday, U.S. Park Police reported.

An autopsy disclosed that Niederriter, Marriott's corporate secretary since 1978, drowned, but police said they did not know how he got into the water.

The body was found at mid-afternoon by police after a passerby discovered his wallet about 25 feet from the Tidal Basin wall, near the John Paul Jones statue. Police said the wallet had no cash in it, but contained several credit cards.

Niederriter's body was fully clothed in a business suit. A wristwatch was on his arm and his personal car keys were in a pocket, police said.

But police said that Niederriter's car was in the driveway at his home at 1779 Red Gate Ct., Rockville, leading police to believe that he might have driven a copany car into downtown Washington. Police said they were searching various Marriott facilities for the company car, but had not found it.

Niederriter, who joined the restaurant and hotel conglomerate in 1969 as an accountant, was last seen at a cocktail party Monday night at the Indian Spring Country Club in Silver Spring.

The party was part of the day-long series of events at the 10th annual charity golf tourney to raise money for construction of the Vincent T. Lombardi Cancer Research Center at Georgetown University. Niederriter had represented Marriott in the golf tourney, according to the company.

Niederriter is survived by his wife and five children.