WASHINGTON (AP) _ There's another ''L'' word out on the political horizon, one that both George Bush and Michael Dukakis would love to lay claim to: Landslide.

Pundits disagree on how lopsided the election returns would have to be to qualify as a landslide, but say they know one when they see one.

''Alf Landon, Barry Goldwater, Fritz Mondale - they are the losers in landslides. ... Those are the compared-to's,'' said Stephen Hess, a senior fellow in government studies at the Brookings Institution.

The numbers were grim for those guys.

1936: Landon was out-polled 61 percent to 37 percent and got eight electoral votes to Franklin D. Roosevelt's 523.

1964: Goldwater lost 61-39 to Lyndon Johnson and collected 52 electoral votes to Johnson's 486.

1984: Walter Mondale went down 59-41 to Ronald Reagan and claimed just 13 electoral votes - 10 from his home state of Minnesota - to Reagan's 525.

William Schneider, a Washington-based political analyst, said Democratic and Republican candidates generally can count on getting at least 40 percent of the popular vote without doing much of anything.

It's the dogfight for the middle 20 percent that makes or breaks a landslide.

''Sixty percent is earthshaking, 55 percent gives you a landslide and you can get a solid majority of the electoral vote with just 52 or 53 percent of the popular vote,'' Schneider said.

Hess believes anything outside the ''47th- and 53rd-yard lines'' is a landslide.

New York Gov. Mario Cuomo's standards are a bit more lax.

''I believe I have defined a landslide as 52 percent (or more),'' he said last week as he predicted Dukakis would win but ''maybe not by as large a landslide as I had figured.''

Richard A. Brody, a political scientist at Stanford University, says the definition of a landslide varies from election to election, and is determined partly by how well a candidate does in comparison with expectations.

''In my characterization, I would say a landslide was an unexpectedly large share of the popular vote for a given candidate,'' Brody said. ''... It's a term of art and people will attribute to it whatever they wish.''

The Dorsey Dictionary of American Politics doesn't play the numbers game, instead defining a landslide as ''a decidedly lopsided political victory, one in which the opponent is metaphorically buried in a landslide.''

It notes that Johnson earned the sarcastic moniker ''Landslide Lyndon'' when he was elected a Texas senator by a majority of just 87 votes out of a million cast.

Dukakis has had to fend off Republicans who ridicule him as a liberal - the ''L'' word - but he is no stranger to the other ''L'' word himself.

In Democratic Massachusetts, he beat his GOP opponents for the governorship by margins of 69 percent to 31 percent in 1986, 60-37 in 1982, and 54-42 in 1974.

But in 1978, Dukakis was stunned when Edward King defeated him 51-42 in the Democratic primary. King went on to beat his GOP opponent by a 53-47 margin - which may or may not be a landslide, depending on whose definition is used.

Bush's double-digit lead in current polls could translate into a landslide - if the numbers hold.

In presidential politics, even a slim lead in the popular vote can translate into an Electoral College bonanza since each state awards all its electoral votes to the popular vote winner even if the candidate wins by just a hair.

As presidential races become increasingly subject to nationwide shifts in candidate popularity, ''we're getting close to the point where a candidate can win 51 percent of the popular vote and carry close to 100 percent of the electoral vote,'' Schneider said.

John White, a former chairman of the Democratic National Committee, noted that Reagan won a modest 51 percent of the popular vote in 1980 to Jimmy Carter's 41 percent, but garnered 489 electoral votes to Carter's 49.

''Under the theory of one man, one vote, or one woman, one vote, it is not fair, but that's the way the law is,'' he said.