A year before they open their nominating convention, the leaders of the Democratic Party believe it will take more than the usual effort to beat President Reagan in 1984.

Deeply disturbed by his policies but confounded by Reagan's political adroitness, the Democrats acknowledge that they need unprecedented self-discipline, a coast-to-coast mobilization of anti-Reagan voters, and--some say--a candidate whose personal appeal is broader than the party's.

This current, for the moment, is running in Sen. John Glenn's favor and keeping Walter F. Mondale from solidifying his front-runner status. Formal surveys and informal talks with those gathered for the final pre-convention meeting of the Democratic National Committee last week showed increasing vacillation between the Ohio senator and the former vice president.

From women activists to southern state chairmen, from labor leaders to black big-city mayors, the Democrats claimed "we have learned our lesson." Their distaste for Reagan and all he stands for is genuine, and they seem determined to avoid the internal divisions that helped Reagan win in 1980.

But as the countdown to the convention begins, two views of the best strategy for defeating Reagan are emerging: one identified with Mondale and the other with Glenn.

The first strategy envisions a "candidate of contrast" who could appeal to those who see themselves as losers under Reagan's regime. That strategy counts on Reagan's driving away millions of his 1980 supporters and the Democrats' registering and turning out millions who did not vote last time.

The phrase belongs to Sen. Alan Cranston of California, but so far the most vocal anti-Reagan constituencies--labor, blacks, women and disarmament supporters--are giving most of their support to Mondale, who increasingly portrays himself not as Jimmy Carter's running mate but as the late senator Hubert H. Humphrey's political heir. The Rev. Jesse L. Jackson, the black civil rights activist, can further splinter that constituency if he enters the race in September, as he was hinting here he will do.

The second strategy puts less emphasis on dumping Reagan and says Democrats must retool their political thinking and pick a candidate whose approach and appeal are not tied to the past. This is the argument of Sens. Gary Hart of Colorado and Ernest F. Hollings of South Carolina and former Florida governor Reubin Askew.

But the new-face, new-pitch philosophy is of most help to Glenn right now. His gains on Mondale were the chief topic of political conversation during the meeting. A drumbeat of state polls showed Glenn closing on Mondale and running better than Mondale against Reagan. Surveys of DNC members showed increased indecision as to who really was the front-runner.

The session was conspicuously devoid of the ideological wrangling and petty nit-picking that many people expect from a Democratic conclave. "These people are incredibly hungry for a win," said Chad Elson, a New York liberal activist.

Reagan has "driven Democratic voters back to our camp, energized our base and given Democrats a passionate reason to turn out," said Bernard Aronson, policy director of the DNC.

Democrats hope that the "let Reagan be Reagan" approach will prevail in the coming GOP campaign.

"Labor, women, blacks, people who care about survival in a nuclear age--he has radicalized them," Aronson said. "These are people who are going to come out and lick envelopes and vote for us."

The belief that Reagan has polarized the electorate underlies one of the Democrats' basic strategies for 1984. They hope to make "the fairness issue" their lever for registering millions of additional blacks, Hispanics and low-income voters, and then turning them out against Reagan.

They had success with this approach in such Sun Belt states as Texas and New Mexico in 1982, where party-coordinated registration and voter-turnout efforts, combining modern technology with old-fashioned populist economic issues, defeated pro-Reagan Republican incumbents.

Though Democrats acknowledge that economic recovery will blunt the fairness issue in some states, the residue of the recession will linger long enough in others for them to benefit.

"This new-found prosperity is being heralded," Detroit Mayor Coleman Young told the DNC, "but here in this city, unemployment is still 20 percent and one-third of our people are still receiving some form of relief."

There is concern about whether the perpetually penniless DNC can scrape together the money and organization it needs to enroll millions of additional anti-Reagan voters. For that reason, the publicity and drama surrounding Jackson's potential candidacy are viewed as an asset, even by blacks and liberal whites who hope he decides not to run. Moves to enlist Jackson as the Democratic registration chairman, rather than as a candidate, were reported during last week's meeting.

At the same time the Democrats press this strategy, they acknowledge being spooked by Reagan's political skill in escaping issue traps and even turning them to his advantage--as they admit he has done with education, at least for the moment.

"There is a kind of awesome disappointment among Democrats, that you hear over drinks or in conversation, that, despite what they see as Reagan's policy failures, he continues to hold up in the polls," California national committee member Bert Coffey said.

It's not going to be easy to beat Ronald Reagan," agreed Georgia state chairman Bert Lance, President Carter's former budget chief. "He's popular with the people."

John Perkins, director of the AFL-CIO's political arm, said he has no doubt that "Ronald Reagan is the strongest candidate they can put up." For that reason, Perkins said, "I'm more optimistic about the Democrats getting back control of the Senate than of the White House ."

Because of their respect for Reagan as an opponent, Democrats are unusually introspective about their own vulnerabilities. With Democrats in Congress already under assault as "big spenders" and "creatures of the special interests," candidates Hollings and Askew bluntly warned the DNC that their party will lose in 1984 unless it sheds those labels.

Mondale and Cranston defended their interest-group links, while Glenn sounded equivocal, describing the AFL-CIO endorsement, for example, as "not the complete albatross some writers say it is."

Despite these differences of tone and tactics, all six declared candidates say the Democrats should run in 1984 as advocates of an activist government. In doing so, they are reacting against not only Reagan's philosophy but also Carter's brand of anti-Washington rhetoric. Carter's name, when mentioned at all, was mentioned critically here.

But the shape, size and direction of that activist government are something on which the Democrats remain murky.

"We know we have to speak to a future that will be very different from our past," Michigan Gov. James Blanchard said. "But it's difficult for a party in transition to speak clearly."

As the economy has begun to recover, Democrats have shifted their rhetoric from assaults on Reaganomics to talk of an "industrial policy" for long-term economic growth, acknowledged as essential for financing all their social programs.

"If you look back at the Philadelphia mid-term convention speeches last June , you see a far different set of issues on the agenda," said North Carolina Democratic chairman David Price. "There is much more attention being paid now to where we go next with this economy."

They know they are groping. "If we have a failure," New York state chairman Dominic J. Baranello said, "it is that we have not come up with our own programs."

Rachelle Horowitz, political director of the American Federation of Teachers and a DNC member, agreed that there is a policy "muddle" but added: "I don't think there's any way it can be unmuddled until there is a candidate. What's the Republican Party without Ronald Reagan?"

Hart has offered himself as the candidate of new ideas, and the DNC endorsed his suggestion for a series of regional candidate forums next year focusing on the issues. But many DNC members find candidate "cattle shows" repetitious and boring.

With polls showing Reagan's popularity recovering as the economy improves, more and more Democratic leaders seem to think they need a personality who can steal a scene from the veteran showman.

This search is helping turn attention and support to Glenn. Mondale, who has the advantage of old loyalties, told committee members he was the best-prepared candidate to face Reagan on the issues, bragging, "I've never lost a debate."

But Glenn's DNC appearance, including a substantive discussion of education policy, helped counter the impression of shakiness on major issues left by his session earlier in the week with the House Democratic caucus. And in their new mood of pragmatism, none of the party leaders missed the significance of Glenn's statement that "I am the Democrat who has consistently run better against Ronald Reagan than anyone else."

That argument cuts heavily with such uncommitted leaders as Angie Evans of North Carolina, president of the Democratic Women's Federation.

"Walter Mondale is the most professionally qualified candidate we have, and he may be able to pull it off," she said. "But I honestly think our only real chance to win is with John Glenn. He's a national hero with national recognition, the closest thing to an Eisenhower in many, many years."