The Heritage Foundation, one of the institutional pillars of the Reagan Revolution, pronounced President Bush a heretic from conservative doctrine yesterday and said that if things went wrong in the country, true conservatives would bear no responsibility for the failures.

"The political void is very real," said Edwin J. Feulner Jr., president of Heritage, the conservative think tank, in his annual "State of Conservatism" report. "We know Ronald Reagan, and George Bush has shown he is no Ronald Reagan."

Burton Yale Pines, vice president of Heritage, said that "the single greatest challenge" facing conservatives is "to rescue" the Bush presidency.

But Pines expressed dismay that Bush might not respond to efforts from would-be rescuers on the right to save him from the Washington Establishment. "Either George Bush wants to be rescued," Pines said, "or he's Patty Hearst and has learned to love his captors."

Heritage's blast is the latest attack on the Bush administration from conservatives, who have been mutinous ever since the president abandoned his no-new-taxes pledge and reached a budget agreement with congressional Democrats last year.

But yesterday's attack carried particular significance. Among Washington's conservative institutions, Heritage has been especially sympathetic to Bush and had actively sought influence within the Bush White House. When other movement conservatives such as Richard Viguerie, Howard Phillips and David Keene were assailing the president, Pines, Feulner and other Heritage voices often spoke up in his defense.

"We were accused rightly of going out of our way to say nice things about Bush, giving him the benefit of the doubt," Pines said in an interview. "We just saw the promise, and I guess we banked on the promise."

Indeed, Feulner's rather gloomy "State of Conservatism" this year contrasted sharply with the triumphal tone of last year's, issued as it was shortly after the collapse of the Berlin Wall and the end of Soviet hegemony in Eastern Europe.

"These are the realities," Feulner said in last year's report, "brought about by the conservative policies of the Reagan-Bush era. . . . "

This year, Heritage has decided that the Bush era has nothing to do with the Reagan era. "The bad news for America, and for American conservatism, is that Washington's power elite -- the Dukakis-style technocrats who believe it is their public duty to tell us how to spend whatever money they allow us to keep -- are clearly in charge," Feulner said.

But Heritage sought to use what it saw as Bush's apostasy as a way of distancing conservatives from the bad news that 1991 is expected to bring. "The further Washington strays from the low-tax, anti-regulatory agenda of the Reagan era," Feulner said, "the worse the economy will get and the better conservatism will look."

In response to questions, Feulner denied that conservatives were trying to separate themselves from Bush at a moment when his administration seemed headed for trouble. He said the current economic slowdown could not be blamed on Reagan's policies, but was instead a response to changes in tax and regulatory policy under Bush.

Charles R. Black, chief spokesman for the Republican National Committee, argued that conservative unhappiness with Bush stemmed almost entirely from the budget deal. "If they look at his performance on other domestic matters, and on defense and foreign policy, they should be happy."

Black added that "rank-and-file conservatives outside the Beltway are happy with George Bush" and predicted that conservatives in and out of Washington would respond positively to Bush's domestic agenda when he outlines it in his State of the Union message next month.

Bush drew a stout defense from the other end of the Republican Party. "On the tax-and-spend issue, Bush was staring down at a deficit that wasn't going away," said William McKenzie, executive director of the Ripon Society, an organization of moderate and liberal Republicans. "No one at our end of the party is wild about tax increases, but at some point, common sense has to come in."