I.F. Stone, former newspaper publisher and nascent Greek scholar, left his study of Pericles and Aristophanes last night to speak about current affairs and to present his first annual Conservative of the Year Award. The winner was named before more than 400 packed into the National Press Club as part of the Institute for Policy Studies' "The Other Side of Town" lecture series.

Stone began by confessing that he had turned down a Playboy magazine request to do an investigative piece on President Reagan--because, he said, there was nothing to investigate. "It's all hanging out. He's ready for the centerfold."

If anyone in the predominantly young, left-of-center crowd expected an anti-conservative broadside, they were surprised by the award. He pointed to what he called a "tidal wave of conservative opposition" to the president, and he presented his group of potential nominees.

Sen. Ernest Hollings (D-S.C.) was one; Senate Majority Leader Howard Baker (R-Tenn.) another. Sen. Robert Dole (R.-Kan.) was nominated for "turning states evidence" on the tax system.

And the winner was . . . the senator from Arizona, Barry Goldwater. "We were all unjust to him," he said. Stone praised Goldwater sincerely. "It's easy to say things your friends want to hear. It takes real guts to say things that annoy your own constituency." Stone cited Goldwater's standing up to the Moral Majority, his bill on cable television and his insistence on giving the Defense budget "a hardy once-over."

About President Reagan he said, "He's an awfully nice guy. I wish he were back at Republic Pictures." He called for a united group of conservatives and liberals to take part in urging the president to say, "Frankly, I made a mistake," and then get him to resscind the tax cut and cut defense spending.