Uneasiness among conservatives about the direction being taken by the Reagan administration broke into the open dramatically here yesterday.

At a gathering of conservative activists, hundreds cheered wildly for a demand that White House chief of staff James A. Baker III be fired, and they gave a standing ovation to a longtime Reagan loyalist who told them Reagan had "defaulted" on his opportunity to move the government to the right.

"There has been no Reagan revolution in Washington," M. Stanton Evans, a conservative writer and lecturer who has supported Reagan since the 1960s, told the annual Conservative Political Action Conference. "There will be no Reagan revolution."

The general reaction was surprising because it came from a group of "mainline conservatives" who have had a long and close relationship with the president. Reagan spoke to the group Friday night in his eighth appearance at the conference in the last 10 years.

The president remains personally popular among the activists. In a poll answered by 683 of the 1,000 delegates, 88 percent said they want Reagan to run for reelection in 1984. Asked to rate his job performance, 32 percent said excellent, 43 percent good, 20 percent fair and 2 percent poor.

But uneasiness among the activists was clearly evident in their responses to conference speakers and by buttons many wore. They said: "Let Reagan Be Reagan," reflecting a feeling among conservatives that Reagan is dominated by moderate aides.

Evans, for example, drew loud applause when he declared, "The president should be asked by all of us and by conservatives all over America to fire Jim Baker."

Of the White House staff, Evans said, "There is not a Reaganite in the bunch."

He appeared on a panel assessing the administration at mid-term with former White House political director Lyn Nofziger and William Rusher, publisher of the National Review.

Nofziger, who started working with Reagan in 1966, conceded that "the results have been mixed" during the past two years. But he reminded listeners that politics is interwoven with compromise and that Reagan "does not have a magic wand that he can wave and get things done."

Rusher was the most supportive of Reagan and warned activists against becoming "macho conservatives" who say "nobody in the room is to the right of me."

Reagan, he said, has shifted the political battlefield in Washington so that "we are not arguing if taxes should be cut, but how much; we are not arguing whether domestic spending should be cut, but how much."

As soon as Reagan leaves the political scene, the Republican Party will "inch back toward the center," Rusher said. Later, he added, "Let us appreciate what we have. Let's follow him . . . . He is our leader. He is a winner."

The poll gave one indication of who the next conservative standard-bearer might be. Asked their second choice for president, 55 percent said Rep. Jack Kemp (N.Y.).

Sen. William L. Armstrong (Colo.) was next with 15 percent, followed by Vice President Bush with 11 percent, Sen. Jesse Helms (N.C.) with 5 percent and Sens. Paul Laxalt (Nev.), Robert J. Dole (Kan.) and Howard H. Baker Jr. (Tenn.) with 2 percent. All are Republicans.

Kemp also spoke to the conference, sponsored by the American Conservative Union and Young Americans for Freedom. He said dissent within the conservative movement was "a sign that we've become the majority."