If Vice President George Bush falls along the wayside on the road to the White House, the albatross of Iran-contra is as likely as anything else to bring him down, according to recent polls. By varying majorities, Republicans and the public at large do not believe his account of what he knew, and when -- and what he did about it.

Even those who take him at his word draw harsh conclusions: he must have been a) terribly dense about the true nature of the arms-for-hostage dealings; or b) woefully ineffectual. Either reading does nothing for his claim to be the man of experience in world affairs who was in the thick of it when the ''tough decisions'' were made. He will have been undone, then, by his failure to put the Iran-contra affair behind him weeks ago with a comprehensive, consistent accounting of his role.

Could be. But Bush's problem has more to do with an earlier, larger mistake. When he began to brandish his re'sume', he should have quit when he was ahead: two terms in the House, envoy to China, director of the CIA, ambassador to the United Nations. It was when Bush began trading on his learning experience in a job that a predecessor, John Nance Garner, wrote off as ''not worth a bucket of warm spit'' that his troubles began.

True, Bush had no way of knowing at the outset that the wretched record of the administration's performance in the Iran-contra affair would be dredged up and laid bare by a presidential review board and a congressional investigation. But that's beside the point. If Bush has only himself to blame for making a test out of a record as vice president, the fact remains: it's a lousy test.

A vice president doesn't have a record. Only nominally can he be thought of as the No. 2 man in the federal government. He is nowhere in the real chain of command. He has no statutory authority other than to break ties in the Senate. "The job of vice president prepares you to be president only in the sense that you are there in case the president dies,'' Norman Sherman wrote the other day in The Post. ''The rest is robotics.''

Sherman is something of an expert on beleaguered vice presidents, having served as press secretary for Hubert Humphrey when Humphrey had, in the Johnson administration's Vietnam War record, his own albatross in the 1968 campaign. Sherman saw Humphrey ''struggling to perform an impossible act of staying close to Lyndon Johnson and far away at the same time'' -- and losing to Nixon. As for Humphrey, Sherman swallows hard: ''I've had 10 years to think of what Humphrey, whom I idolized, did as vice president. It all adds up to zero.''

Bush is in no better shape than Humphrey was to have it both ways -- to pump up his vice-presidential experience while bobbing and weaving when it comes to the particulars. No more than Humphrey could take his distance from Johnson by airing publicly whatever differences he conveyed privately on Vietnam can Bush do the same with the Iran-contra affair -- not for the ''precedent'' it would set, but as a matter of principle and practical politics.

To be sure, Bush has problems Humphrey didn't have. Public investigations have caught Bush up in a mass of glaring contradictions. Not the least of them has to do with whether he was even present at one critical meeting on Jan. 7, 1986, when secretaries Shultz and Weinberger conveyed to the president their vehement opposition to any sale of arms to Iran, let alone sales linked to the release of American hostages.

The Tower review board, the report of the congressional investigators and Shultz all say Bush was there. Bush says he ''probably'' was, but maybe not all of the time -- and that, in any case, he surely would have remembered if Shultz had been all that exercised. The president has wonderfully complicated the case by stating categorically that Bush was ''not present.''

Having once thought that Bush could easily clear all this up, I'm increasingly convinced that the vice president should try a different defense: plead guilty to being vice president -- and ask for clemency. He could argue that, more often than not, his long look over the shoulder of the Reagan administration at work has been the best kind of on-the-job training for how not to conduct foreign policy.

He could even borrow a line from Norman Sherman: the vice presidency, he might say, ''is a job of no consequence, of few real and many quite forgettable accomplishments and, more's the pity, of self-delusion that you are an irreplaceable player in important acts of state.''