The National Gallery of Art announced yesterday that it has received control of $3 million from a fund set up by the late Lila Acheson Wallace, co-founder of Reader's Digest. The money will be added to the museum's Patrons' Permanent Fund, a primary source of income for the purchase of major works of art.

More than $2.6 million of the donation from the $550 million Lila Wallace-Reader's Digest Fund was invested in the 1980s for the gallery's benefit. Those funds have now been placed under the museum's control.

The museum receives its operating funds from congressional appropriations ($40.5 million in fiscal 1989) but uses no government money for acquisitions. All its art has been either donated or purchased with funds given by individuals, foundations or corporations.

The Patrons' Permanent Fund was set up in 1981, when it became clear that the National Gallery had to broaden its base of support beyond that of the founding Mellon family, which had paid for both its buildings and also had bought many of its most important pictures.

The original goal of the Patrons' Permanent Fund was $50 million, to be contributed by wealthy donors. By the end of fiscal '89, the fund had reached $71.9 million.

In today's market, the entire patrons' fund could be exhausted by the purchase of a single picture.

Several important paintings have already been acquired with income from the patrons' fund. These include "The Fall of Phaeton," by Peter Paul Rubens, purchased in May for an estimated $3 million; Rembrandt Peale's "Portrait of Rubens Peale With a Geranium," purchased at auction in 1985 for $3.7 million; Andrea Mantegna's "Entombment"; Benjamin West's "Expulsion of Adam and Eve From Paradise"; and Francis Picabia's "Machine Tournez Vite."

Wallace was even more generous to the Metropolitan Museum in New York. Her foundation paid $11 million of the $26 million cost of the Lila Acheson Wallace Wing for 20th Century Art, added in 1987.

Some of her other endowments to the Met were used to renovate and maintain the museum's Great Hall and to provide the lavish bouquets of fresh flowers in the lobby.

While they lived, Wallace and her husband, DeWitt, gave $200 million to New York institutions. Lila Wallace died in 1984; DeWitt Wallace died in 1981. Last year her foundation distributed $13.8 million, a sum expected to rise to $20 million in 1991. The foundation's assets increased significantly following the public issue of Reader's Digest stock last year.