Like a vaudevillian feeling out the audience in a new town, Henry Kissinger tried a bagful of theatrical devices in Detroit today. He shifted from the cheerleader for Ronald Reagan to the proud defender of his own past and back again, not always looking comfortable with the faces in the crowd.

For the conservative delegates to the Republican National Convention -- many of whom joined happily in denoucing Kissinger's foreign policy four years ago -- the former secretary of state had a carefully drafted statement of contempt for Jimmy Carter's foreign policy and an endorsement of Ronald Reagan as "the trustee of our hopes."

As delivered by Kissinger, it was a flat speech, one that failed to hold the attention of many delegates in the hall. A threatened demonstration against Kissinger never materialized, but neither did much enthusiasm for the former secretary of state.

Kissinger did not reach the podium in Joe Louis Arene until nearly midnight, almost two hours behind schedule. Earlier, at a press conference, Kissinger could not disguise his reservations about Reagan's past statements on foreign policy. Kissinger's almost instinctual desire to distance himself from the candidate was unmistakable.

"We discussed primarily those issues that had given me some concern," Kissinger said at the press conference, referring to his meeting this morning with Reagan and his key aides at the Plaza Hotel here. "I felt that the governor's position as it was explained to me was one that I find compatible with my own."

At a buffet lunch hosted by Arthur Ochs Sulzberger, publisher of The New York Times, a reporter who knew Kissinger well when he was in power teased him about his predictions then that if the Vietnam war did not end well for the United States there would be a fierce right-wing reaction in the country.

"It turned out just about the way I predicted it would," Kissinger quickly replied.

Through it all, Kissinger anxiously sought to protect both his self-esteem and his ambitions. He avoided any praise of Reagan as a potential diplomat and statesman, apparently on the grounds that he felt he would like an apple-polisher if he gave praise that he didn't really believe was justified. And by all indications. Kissinger's low opinion of the foreign policy advisers around Reagan did not go up as a result of his experience here today.

But Kissinger told Reagan personally, the press conference, the full convention and friends in private conversation today that it was "in the national interest" for Reagan to defeat Carter in November.

Kissinger had no doubt about that, even if Reagan was his third or fourth choice for the Republican nomination this year, and despite the former California governor's lack of experience in world affairs.

The Reagan camp gave Kissinger a respectful reception here. Several sources close to the former governor said they were sure that Kissinger would "play a role" in the campaign and in a Reagan administration, but it did not sound like a very important role.

During his address tonight, Kissinger's wife, Nancy, and Nancy Reagan, sitting side by side in the gallery, carried on an animated conversation. Neither Nancy paid any attention to the former secretary of state as he spoke.

The prospect that he might be booed or badly received had bothered the notoriously thin-skinned Kissinger all day. Yet he was treated like a celebrity wherever he and his bodyguard went, with crowds forming spontaneously to cheer him, and people asking him for autographs. He clearly enjoyed the attention.

And his manner was Kissingerian throughout. Leaving this morning's press conference, where he had made clear his own reserve about Reagan without ever needing to spell it out, Kissinger threw an arm around James Brady of Reagan's staff, who had accompanied him to the meeting with reporters, and said with a questioning expression but an assertive tone: "There wasn't anything embarrassing for you in there."

According to Kissinger, he told Reagan in advance that he wanted to avoid any talk today about jobs in a Reagan administration. "I'm not here as a job-seeker," Kissinger insisted.

His modesty on that point probably wasn't surprising. Reagan now has a list of about 100 foreign policy "advisers," but Kissinger's name does not appear on the list. Many of the names that do appear belong to men who are bitter adversaries of the former secretary of state.