Henry A. Kissinger is scheduled to speak to the Republican National Convention Tuesday night, a prospect that has him a little nervous and at least a few conservative politicians here talking about a protest.

At the 1976 GOP convention, Kissinger unwittingly played the role of pin-cushion to the needles of rightwing Republicans angered by his brand of diplomacy. Much of the foreign policy section of the 1976 platform was an implicit criticism of that diplomacy.

Since then, Kissinger's line has hardened appreciably, and in interviews here today he said he supports "the main directions" of the toughly-worded 1980 platform that the Republicans will adopt this week.

Asked tonight what he will do if there is a demonstration when he comes to the podium here, Kissinger replied, "It's not my problem." What will he do if there is booing? "That will be up to the chairman" of the convention, he replied.

After these responses, though, Kissinger's expression changed and he asked a reporter if there was a serious prospect of a demonstration. He seemed eager for information.

In fact, aides to Sen. Jesse Helms (R-N.C.), who led the criticism of Kissinger at the 1976 convention, today backed off from threats that they would organize an anti-Kissinger demonstration, telling reporters that this is "a unity convention." But there are persistent reports that others are considering some show of displeasure when Kissinger appears.

In an interview with Walter Cronkite of CBS, Kissinger gave a hint of his own status vis-a-vis the Reagan campaign, which has chosen not to include him in its long list of foreign policy advisers. "I haven't had any conversation with Gov. Reagan since last October," Kissinger said.