Conservative activists were sharply divided yesterday over whether they want Rep. Jack Kemp (R-N.Y.) or Vice President Bush to succeed President Reagan as leader of their movement as they ended a three-day meeting here.

Kemp, a longtime conservative favorite, defeated Bush, once regarded as a moderate, as the 1988 presidential favorite in a poll of the 12th annual Conservative Political Action Conference. But his margin was far smaller than expected, 39 percent to 35 percent.

The poll came as Kemp prepared for a political excursion to New Hampshire, and Bush, who has taken an increasingly important role in Reagan administration diplomacy, prepared for a major African trip with political overtones.

Sen. Jesse Helms (R-N.C.) placed third among the 269 answering the poll, with 10 percent; Democrat Jeane J. Kirkpatrick, the former ambassador to the United Nations, was fourth with 4.5 percent. Two potential GOP contenders, Senate Majority Leader Robert J. Dole (R-Kan.) and former majority leader Howard H. Baker Jr., received no votes.

"Clearly Kemp has the emotional and personal support of many activists, but he doesn't have a consensus yet," said David A. Keene, chairman of the American Conservative Union, a sponsor of the event. "On the other hand, George Bush has been vice president for more than four years and he is regarded as a loyal and able spokesman for President Reagan."

Robert E. Dolan, chairman of Young Americans for Freedom, another sponsor, said Bush, once widely suspect among conservatives, made a "surprisingly strong showing."

He attributed it to "a growing perception that Bush is becoming more conservative, or he is allowing his conservative instincts to guide his policy."

The conference, traditionally the year's most prestigious gathering of conservatives, took place at a time that William A. Rusher, publisher of the National Review, called "the golden age of American conservativism."

"The liberals are in a state approaching moral collapse. They know their policies were tried thoroughly. They know they failed miserably," he said. "We have acquired psychological dominance."

But the conference demonstrated that some of the sacred cows of the political right, including increased defense spending, are beginning to fail. Sen. Charles E. Grassley (R-Iowa), a longtime conservative, was applauded loudly when he attacked wasteful procurement policies at the Pentagon and called for a freeze in defense spending, for example.

Conservatives polled said they considered strengthening national defense less important than cutting taxes, balancing the budget, fighting crime and "protecting the unborn" during the next four years. Some said they no longer support the MX missile.

Kemp was cheered loudly when he attacked another conservative favorite -- corporate tax incentives. "There is no reason conservatives should support tax breaks and subsidies for corporations," he said. "There's no reason for corporations to be subsidized by government."

The gathering attracted a potpourri of conservative groups, selling their causes, heroes and ideas. On sale were "Kemp for President" buttons and bumper stickers saying, "We Are for Free China" and "Grenada: The Media's Lost War."

The speakers included Reagan and some of the nation's most articulate conservative spokesmen. But questions from the audience indicated that many activists are operating on a different plane than their leaders.

Donald T. Regan, the White House chief of staff, seemed particularly at a loss about what to say to one woman. She suggested that the arrest of 40 persons in Minnesota for child abuse was part of a homosexual plot to discredit family life. Regan said the president is against "oddball groups."

When a young man suggested to Rep. Newt Gingrich (R-Ga.) that space exploration was best left to private industry and market forces, Gingrich replied, "That's exactly how Herbert Hoover took us down the wrong road."

Gingrich argued that conservatives adopt space exploration and Reagan's Strategic Defense Initiative, the so-called "Star Wars" program, as causes for tactical political gain. "Young people like space," he said. "Young people like the future."

The mood of conservatives was upbeat as they looked at the present and discussed how to solidify their gains. Rusher, one of the intellectual leaders of the movement, warned activists not to fall into old traps.

In a keynote address, he said that conservatives are in a rare "period of dominance and unity. Temperamentally, there are some who can't stand that. They have a siege mentality. They can't stand success."

But it was Rusher's attacks on liberals that drew the most enthusiastic applause. For decades liberals held "the high moral ground" against the conservatives, but they have lost it, he said.

"They simply have no answers. They've tried everything in the book," Rusher said, adding that liberals have been reduced to getting their "quick moral fixes" by being arrested in front of the South African Embassy.