Abram (Al) Lerner, founding director of the Hirshhorn Museum and Sculpture Garden, will retire from his post next May.

"I think it is the proper time," said Lerner, who supervised the Hirshhorn's growth from a private art collection into a national museum of modern art. "I will be 71 next April. I've done everything I could. I helped create the museum, I helped select its staff. What more can I do? If I were 20 years younger, I'd love to stay."

The Smithsonian Institution has appointed a committee to search for Lerner's replacement.

Lerner owes his job to the friendship he formed in 1945 with Joseph Hirshhorn. Lerner, who in those days hoped to be a painter, had just taken a job in Manhattan's ACA Gallery, a favorite of Hirshhorn's, when "Joe burst into my life."

Lerner has told the story often: "This little tornado stormed in. He never gave his name. He said, 'You be a good boy, and I'll take that one, that one, that one and that one.' Then he left. I had no idea who he was. I thought the keepers were coming to get him."

Despite Hirshhorn's brashness and Lerner's courtly manner, the two had much in common. Both grew up among the Jewish immigrants on New York's Lower East Side, and both loved art. Lerner, who had graduated from New York University into the mural project of the WPA, soon became Hirshhorn's art scout and adviser. "And for some reason or other," Lerner said, "we became close friends."

In 1955, Lerner quit the ACA and, funded by a Hirshhorn Foundation grant, set off to study art in Europe. In 1957, shortly after his return, Hirshhorn named him curator of his expanding collection. In 1958, Lerner had his first--and last-- one-man show in New York. Thereafter, until Hirshhorn's death in 1981, the two men were a team.

In 1966, during a meeting with President Johnson, Hirshhorn pledged his art for a museum on the Mall. Lerner was part of the deal. "Some people didn't want him because of his lack of experience directing a museum," Hirshhorn once recalled, "but I insisted on it. They didn't accept that, it would have been bye-bye Charley."

Lerner was named director of the not-yet-formed museum in 1967. It opened to the public in October 1974. "It was a very rough time," Lerner said. Foes of the museum, some of whom were vehement, said Hirshhorn's art was second-rate and that his choice for director could not handle such a job. Time proved the critics wrong on both counts.

Under Lerner's guidance, the doughnut-shaped museum has mounted more than 40 loan exhibits. And many smaller shows drawn from the collection have made evident the wide range and high quality of Joseph Hirshhorn's art.

Hirshhorn founded the museum with a 6,000-work donation. An additional 1,500 works have since come to the museum through purchases and gifts, and, at Hirshhorn's death, he left 6,000 more.

Lerner's retirement "will deprive us of one of our most illustrious colleagues," said Smithsonian Secretary S. Dillon Ripley. "The museum can never be anything but an institution that bears his imprint," said Sen. Daniel Patrick Moynihan (D-N.Y.), chairman of the Hirshhorn board.

"I'll probably retire to Southampton, N.Y. ," said Lerner. "I'll look at a lot of art. I'll read a great deal. I'll study and I'll write. I won't miss the building. I'll miss the staff. I hope some of them will sometimes think of an old, feeble, former museum director somewhere in the Hamptons, sunning himself in old age."

Chairman of the search committee will be John Reinhardt, the Smithsonian's acting assistant secretary for history and art. Its members will include Charles Blitzer, whom Reinhardt replaced; Anne d'Harnoncourt, director of the Philadelphia Museum of Art; Thomas Messer, director of New York's Guggenheim Museum; Henry Hopkins of the San Francisco Museum of Modern Art, and two Hirshhorn trustees, businessman and collector Sydney Lewis of Richmond and Jerome Greene, a New York attorney.