Charity art auctions do much good -- but not for the living artists whose works go on the block.

Such auctions do have winners: The worthy cause is one; it receives needed cash. The buyer is another; if lucky, he may get a bargain that he likes--and a tax deduction, too. And the audience has fun. Perhaps the only loser is the poor artist. Though often asked to donate his art, he gets little for his trouble. First he gives away his work, and then he may be embarrassed by the low price that it brings. And, under current law, his only tax deduction is the cost of his materials.

In Washington this year, that unfair situation has at last begun to change.

Consider, for example, the charity art auction that will be held tonight at 7:30 at the Montrose School on R Street between 30th and 31st streets NW. Run by A. Salon Ltd., the nonprofit art cooperative, it will raise money for the New Horizons art program of the D.C. Children's Hospital and for the Fillmore Arts Center, a D.C. public school. Admission is $5. Works by 57 artists--among them Gene Davis, Sam Gilliam, Alan Sonneman, Sarah Tuft, Ron Rose, Mark Power, Patrice Kehoe, Kevin MacDonald and Tom Green--will be offered.

What makes this auction different is that the artists will get something for their art.

Say a picture sells for $100. The artist will get all of that--and then will donate half his take, in cash, not in art, to the charities involved. A. Salon, the agent, will take no commission. Since most commercial galleries take a 50 percent commission, the artist will receive his usual percentage. True, his art may go for less than it is worth. But auctions are unpredictable. It may fetch more.

Patricia Helsing, who organized tonight's sale, says she has cleared the system with the IRS.

Other institutions which hold charity art auctions now are beginning to offer artists something in return.

The First Annual Brandeis Art Exhibit and Sale was held here, at the Forrestal Building, last Saturday. It earned money for Brandeis University, but did not misuse its artists: 460 applied; a jury accepted 70, and gave each a small solo show. Prizes totaling $800 were given to participants, and an audience of 1,400 saw their exhibitions. The artists were given 80 percent of the money that their art brought in; 66 works were sold for a total of $25,000. "We didn't earn all that much from the sale," said chairman Anne Abramson, "but we made out all right. We sold 900 tickets, we put on a good show, and we didn't do it on the backs of the artists. Olga Hirshhorn bought three pieces, and I don't think the artists who made those sales will ever be the same."

The Corcoran School of Art held an "Affordable Art Auction" last June. With the late Joseph H. Hirshhorn and Olga acting as auctioneers, 213 pieces sold for a total of $70,000. All of them were donated. But this year's auction, to be held June 9 and 10, will let participating artists retain half the money that their pieces fetch.

On April 1, 1981, the Fillmore Arts Center held an auction of 300 donated works of art at the Foundry Mall in Georgetown, and netted $14,000. Tonight's auction, however, will not depend on such donations. (Each week the Fillmore teaches 888 students from six public schools. A worthy institution, it has just won a $10,000 Rockefeller Brothers Fund Award in Arts Education. It was one of only 10 schools, out of 45O applicants, to receive that award.)

The Washington Project for the Arts has held two art auctions. The first, in 1980, brought in $4,000. The second, held last May 29, grossed $40,000. All the 150 pieces sold came in as donations, most of them from artists. "We're not sure it's a good idea to accept such gifts from artists, but the feedback we get from the art community is that they want to give art," said Joy Silverman, one of the WPA's assistant directors. "They don't have much money, or much time, but they want to help. It's a tricky question. We expect to hold another auction next Nov. 19. We're not yet sure how it will be run."

Artists, understandably, rarely donate their best works to charity art auctions. They can't afford to. The new system, though it may do some damage to commercial dealers, has one distinct advantage for those who buy at auctions. Because artists know they stand to earn money from such sales, they tend to make available their better works of art.