Democratic presidential candidates are running hard earlier than ever, with former vice president Walter F. Mondale performing the political equivalent of ripping a telephone book in half and Sen. Alan Cranston, a long shot, taking a big early gamble by vowing to outshine the others this weekend in a political beauty contest in his home state of California.

The ambitious Democrats generally are raising more money, are better organized and are planning formally to announce their candidacies earlier than ever, even though the Democratic Party 10 months ago adopted rules aimed at shortening the ever-lengthening presidential marathon.

This weekend in Sacramento, where the annual California state Democratic convention has been transformed into the 1984 election's first candidate "cattle show," the presidential campaign begins unfolding publicly for five men who are already working nonstop to be the next president, and for two more who say they are thinking about it.

In addition to Mondale and Cranston, those who will court the delegates and address the convention are Sens. John Glenn of Ohio, Gary Hart of Colorado, Ernest F. Hollings of South Carolina and Dale Bumpers of Arkansas and Rep. Morris K. Udall of Arizona.

Udall and Bumpers have yet to decide if they'll run. Former governor Reubin Askew of Florida, who plans to announce his candidacy formally on Feb. 23, declined the California invitation.

Mondale has been the front-runner in the national polls of Democrats' presidential preferences since Sen. Edward M. Kennedy of Massachusetts withdrew last month.

A Gallup Poll released yesterday showed Mondale as the choice of 32 percent, with 14 percent for Glenn, 6 percent for 1972 standard-bearer George McGovern, so far not a candidate, and 5 percent for former California governor Edmund G. (Jerry) Brown Jr., who says he is not running for anything. The others were at 3 percent or less.

With the choice narrowed to Mondale and Glenn, 59 percent of the Democrats pciked Mondale, 28 percent chose Glenn and 13 percent were undecided.

The two ran even with independents, who make up a fourth of the electorate and can vote in some states' primaries, with Mondale at 41 percent and Glenn at 40 percent.

The Gallup Poll, taken last week, showed both Mondale and Glenn beating President Reagan if the election were now, Mondale leading 52 percent to 40 percent, Glenn 54 percent to 39 percent.

Mondale also was the leader in a December survey by Penn and Schoen Associates, taken for political consultant David Garth. Mondale was the choice of 42 percent. Glenn was second with 18 percent, and Udall third with 8 percent.

As they prepared to roll their bandwagons westward, the candidates paid private tribute to Mondale's first accomplishment of the year, which had little impact on the public but impressed the pros.

The feat was to raise in just 48 hours more than twice as much money as necessary to qualify for federal matching funds. Under the federal campaign laws a candidate has to raise $100,000, $5,000 each in at least 20 states in single contributions of no more than $250. Mondale raised more than $200,000.

"Mondale's quick qualifying was a cute gimmick, but it was impressive," conceded Robert Keefe, Glenn's most seasoned adviser. "The new contribution limitations make fund-raising the supreme test of organizing. This shows they know the name of the game."

Cranston's campaign manager, Sergio Bendixen, concurred.

"It's impressive because, in all honesty, we were trying to do it as soon as possible, too," he said. Cranston's organization raised $120,000 in 10 days and was pleased to come in second.

Cranston will not be pleased to finish second at the convention here, however. The Los Angeles Times is polling the nearly 2,000 delegates on their presidential preferences, and state party officials apparently are bowing to Cranston's wish that the party conduct its own poll of the delegates.. The Cranston forces have worked the delegates as if this were a national nominating convention.

Bendixen predicted that, while the undecided or uncommitted vote may top the pack, Cranston will finish higher than the others.

And he conceded that anything less than a victory in his home state would seriously damage the Cranston campaign.

The fact that a straw poll is even being taken so early has put Cranston in a no-win situation, many Democrats believe. A win in his home state is expected, and a loss could be shattering.

Last November Cranston began politicking the party's assembly district caucuses, where a portion of the state convention delegates would be selected. Cranston toured the state, lining up 50 to 60 commitments a day, Bendixen says.

Cranston's advisers are convinced that the convention is their chance to gain national recognition, which has not yet come the senator's way.

Mondale's advisers are pleased about the Los Angeles paper's straw poll.

"From our point of view," says his chief adviser, James Johnson, "anything which builds interest and focuses on the candidates now is very useful."

All the candidates but Glenn are operating under the traditional assumption that they have to show well in the first contests, the Iowa caucuses, which have been set back from late January to the last week of February, and the New Hampshire primary, which is scheduled a week later, on the first Tuesday in March.

Glenn's advisers say he will run hard in New Hampshire, but they are not sure he will make an all-out effort in Iowa because Mondale and others, notably Hart, already have strong organizations there.

Glenn is focusing on the week after New Hampshire, when primaries and caucuses are scheduled in seven states, including several in the South. Glenn, a moderate, hopes to mount a strong challenge to the southern candidates.

"It's World War III," says Keefe. "It will in a large way determine who will be the nominee. Unlike Iowa and New Hampshire, you can't campaign in all of those states like you are running for sheriff."

Keefe cites President Reagan, who did not campaign in Iowa in 1980, as proof that it is not necessary for a candidate who is otherwise well-known to win there.

Not since 1964, however, has a major party candidate, other than an incumbent president or vice president, won the nomination without winning in New Hampshire.

The candidates are also focusing on an even earlier crucial contest. The AFL-CIO hopes to unite its often splintered unions in endorsing a Democratic presidential candidate next December, before any primaries and caucuses.

Mondale is playing to win labor's endorsement, the others are playing to block him.

With Kennedy out, Mondale is the undisputed favorite for the endorsement, but it is possible that he will fail to get the necessary two-thirds majority. The federation wants most of all to back a winner.

"Labor is reasonably comfortable with Glenn--he has good labor support in Ohio, and I think they think he has the best shot at winning a general election," Keefe said. "But the personal relationships John Glenn has with labor's leaders don't compare with Fritz Mondale's."

Glenn and Cranston may work together to block a labor endorsement or at least delay it until after the first big week of primaries.

"Labor does have great strength in Ohio and California," Keefe said, "and that may be a great team to stop anyone from endorsing early."

Mondale already has put together an impressive organization, much of it a carryover from the Carter-Mondale campaigns of 1976 and 1980.

But Hart has scored what some consider significant coups by luring Chris Brown, who skillfully organized New Hampshire for Carter in 1980, and Bill Romjue, who did the same for Carter in Iowa. Hart also has signed Lynn Cutler, who was narrowly defeated in a congressional race in Iowa.

Glenn's candidacy has been fueled by his high name recognition as an astronaut. He trails the others in organization, however, largely because he did not allow major efforts to begin until he decided to run.

This week he hired a former Carter campaign and White House assistant, Greg Schneiders, as his press secretary, and Bob Farmer, a former Kennedy assistant, as his chief fund-raiser. He is still looking for a campaign manager.

Hollings has scored strongly in recent outings after a slow start. He has made several strong speeches after a poor showing at the party midterm conference in Philadelphia. His staff, after some early slips, blitzed New Hampshire with letters and phone calls and turned out large audiences for receptions there this month.

Askew, the only candidate not attending the Sacramento convention, has nevertheless traveled widely. He visited all 50 states by the middle of last year, and his spokesman vows, "Governor Askew will disappear into the cornfields of Iowa and the rocky crags of New Hampshire" in an effort to do well early on his way to the primaries in the South.

Cranston has amassed an impressive list of New Hampshire names and intends to campaign on the issues of peace and curbing the nuclear arms race. But his Iowa efforts lag, chiefly because he put his faith in his friend, former governor and senator Harold Hughes, whom Kennedy lured away just days before Kennedy withdrew.

Udall, who is weighing a run after an unsuccessful bid in 1976, is buoyed by his unexpectedly strong showing in the Penn and Schoen poll, but he suffers from Parkinson's disease. Bumpers is bringing a entourage of modest size with him in his exploratory effort that is late by contemporary standards, even though more than a year remains until the primaries.