Ronald Reagan is now in a singular position to offer advice and help to President Bush, but if history is a guide he may not be called upon to do so very often.

"Bush has got to establish himself as America's leader," says Thomas E. Cronin, professor of American Institutions and Leadership at Colorado College and author of "The American Presidency.""He's going to have a major problem on his hands in starting to govern because people will compare him to Reagan, who remains very popular. It will be almost a disincentive to call on Reagan."

Bush has not said to what extent he will rely on his predecessor. His spokesman, Marlin Fitzwater, did not respond to an inquiry about the subject.

But if Reagan plays any important role in decisions of the new president, he will be the exception to the rule.

"One comes away from even a cursory review of the lives of ex-presidents with a chilling sense of a wasted resource," former Deputy Secretary of State Warren Christopher said in 1986 at the dedication of the Carter Presidential Library in Atlanta.

"On the whole, their experience was undervalued and their advice too little sought," Christopher, a Los Angeles attorney, said.

Christopher said one important reason was "partisan zeal" - the reluctance of Democratic presidents to appear dependent on Republican predecessors and vice versa.

This does not, however, explain such things as Reagan's meager public contact with former Republican presidents Nixon and Ford.

Reagan did confer privately with Nixon but, Cronin said in a telephone interview, "kept him at a distance." Reagan had good reason to avoid being linked publicly with the president forced to resign by the Watergate scandal.

As for Ford and Carter, said Cronin, Reagan had "no contact" with them except for the time he sent all three living former presidents to represent the United States at the funeral of Egyptian President Anwar Sadat.

Some former presidents have been used more substantially.

Franklin D. Roosevelt ignored his arch-rival Herbert Hoover, but Hoover coordinated postwar relief for President Truman and both Truman and Eisenhower named him to commissions to streamline the government.

John F. Kennedy conferred with Eisenhower at Camp David after the debacle at the Bay of Pigs.

John Quincy Adams served 17 years in the House after leaving the presidency, and William Howard Taft became chief justice.

On the whole, however, said Christopher, "the former presidents and indeed the nation have groped uncertainly for a proper role."

Now, for the first time since 1861, there are four of them - Nixon, Ford, Carter and Reagan. Like the other former presidents, Reagan gets an office allowance.

"Many Americans would ask, `Why do we let these four people wander around the country playing golf and pushing their books? Why aren't they serving the public?' " said Cronin. "A lot of Americans say we ought to be getting more out of them than we are getting."