A federal grand jury charged yesterday that the director of maintenance for the D.C. Department of Recreation and a chief mechanic used about $580 in department funds to buy a car transmission, installed on the director's 1974 Lincoln Continental, and two sets of tires.

A 22-count indictment returned yesterday in U.S. District Court also charges that the two employes and a third man later conspired to conceal the transmission purchase from law enforcement officials who have been investigating possible illegal use of department property since last March.

Maintenance director Howard F. Gasaway Sr., 50, a department employe for 25 years, and chief mechanic Julius L. Johnson Sr., 58, were both placed on leave without pay, a city hall spokesman said.

According to the 33-page indictment, Johnson used phony recreation department purchase orders to buy a rebuilt transmission. The grand jury alleged that Johnson also used recreation department funds to buy two sets of whitewall radial tires, at least one set of which was used on Gasaway's car. The transactions took place between February and May 1978, the grand jury said.

Last summer, after learning that investigators had uncovered documents about the transmission purchase, Gasaway and Johnson devised a scheme to buy another, decoy transmission, which Johnson eventually turned over to the D.C. police, the indictment said.

The grand jury charged that a third man, Herbert Lewis, 36, described only as a close friend of Gasaway's 26-year-old daughter, bought the decoy transmission at a Glen Burnie, Md., transmission shop.

Gasaway, Johnson and Lewis all were charged by the grand jury with conspiracy to obstruct justice in connection with the alleged cover-up.

The indictment also charged that Lewis and Johnson made false statements to the grand jury in connection with its investigation into the purchases.

Gasaway, who lives at 2806 32nd St. SE, has been maintenance director for two years, supervising more than 200 employes. Johnson, who supervises the purchase of large quantities of automotive parts for recreation department vehicles, lives at 1015 Booker Dr., Seat Pleasant. Lewis, who is not employed by the recreation department, lives at 3413 South Kemper Rd., Arlington.