He came to town two years ago, a bespectacled, largely unknown Los Angeles lawyer-banker. If people wondered anything about Charles T. (Chuck) Manatt, it was why a successful, self-made millionaire would have worked as hard as Manatt did after the 1980 election to outdistance four rivals for the dubious honor of taking over the debt-ridden Democratic Party in the wake of its worst defeat in a generation.

Today, with the Democratic National Committee in the midst of its annual winter meeting here this weekend, its chairman remains largely anonymous in the capital, but he is no longer inconsequential.

Manatt, 46, has consolidated his grip on the Democratic headquarters and has put himself in a position to play a major role in what happens to his party and its candidates at least through convention time in the summer of 1984.

From the "down-draft" he says he felt when he took over in February, 1981, "a time when we had no idea who we were or what we were up against," until today, Manatt has witnessed a revival of his party's political prospects, which many party activists attribute in part at least to his stewardship.

Among the accomplishments for which he receives a share of the credit from Democratic governors, members of Congress and state party officials:

* A midterm election rebound, including a strikingly successful demonstration project in state party-building that will serve as a model for the 1984 contest.

* A healthy start on a direct-mail fund-raising mechanism that could, in time, cut down the Republicans' still-growing financial advantage.

* Negotiation of the formal return of organized labor as a participating and contributing part of the Democratic Party and partial repair of the Carter-era breach with business and the Jewish community.

* The peaceful acceptance by the party's women, minority and liberal caucuses of a substantial revision in the delegate-selection system, which will set aside one-seventh of the seats at the 1984 convention for members of Congress and other elected and party officials, whose voices may dilute the influence of the grass-roots activists.

* A thin but reasonably noncontroversial outline of a Democratic policy alternative, given public exposure in a harmonious midterm conference, campaign ads and the coordinated responses to President Reagan's television and radio speeches.

To cap off this effort to reassemble the elements of the Democratic coalition that fell to quarreling in the 1970s, Manatt expects to announce within a month firm plans for financing and constructing a long-sought Democratic headquarters building on Capitol Hill, the first permanent home in the long history of the nation's oldest party.

"Little by little," said one Democratic congressional leadership aide, "Chuck has accomplished quite a lot, maybe more than he gets credit for."

One reason for the lack of credit may be Manatt's stiffness as a spokesman for the party. His speeches, though earnest, rarely soar, and his style in interviews and news conferences is pallid when compared with that of his two Texas predecessors in the chairmanship, John C. White and Robert S. Strauss.

Strauss' continued high-profile presence on the Washington scene is a particular problem for Manatt, who contested the flamboyant Texan for the party chairmanship a decade ago and lost.

Paradoxically, Manatt's public statements over the last two years rank among the most consistent and strongly worded indictments of the record and intentions of the Reagan administration.

On Jan. 23, 1981, three days after Reagan was inaugurated and while Manatt was still campaigning for his job, he told the Democratic state chairmen that "there can be no honeymoon era for Ronald Reagan Republicanism," which he characterized as "people who dress their wives in minks and $10,000 dresses cutting programs for the aged and the children."

He never relented, nor did he mince words when many other Democrats were granting Reagan that honeymoon.

At the National Press Club, less than a week after the assassination attempt on Reagan, Manatt moved in seven paragraphs from expressing his wishes for a "speedy recovery" to voicing his conviction that "Republicans have a hidden agenda. In the name of fighting inflation and stimulating the economy, they are attempting to roll back 50 years of progressive tax and social policy. They want more for the rich and less for the average American family."

"I knew these people," Manatt says now of the Reaganites, "and I knew where they were coming from, even if other people didn't back then. I had seen them operate in California, and their view is that 'we got ours,' and everyone else ought to shift for themselves. They think if you go to the government for help, you're not as strong and not as virtuous as they were."

This kind of populism came naturally to the Iowa farm boy who worked his way through George Washington Law School with a job at the Democratic National Committee as executive secretary of the Young Democrats and once was fired from its staff in an economy move.

But it sounds strange to many people coming from a Century City bank president and senior partner in an aggressively expanding law firm with lots of high-powered clients.

Manatt insists there is no paradox.

"I never got the GI bill or a VA loan for myself," he says, "but I believe in government as a way in which we help each other cooperate in this country. In my mind, I'm an Iowa farmer, and when the American Banking Association voted in 1981 on endorsing the Reagan tax bill, I was outvoted 400 to 6."

Despite opposition by Senate Minority Leader Robert C. Byrd (D-W.Va.) to formation of a DNC policy arm, Manatt has been able to work cooperatively with Hill Democrats in orchestrating an effective Democratic propaganda attack on such issues as Social Security and the recession, using some paid advertising but relying mainly on the free response time the networks have granted Democrats to answer Reagan speeches. The line, "It isn't fair--it's Republican," came out of one of the Manatt-financed ads.

Every couple of months, he presides at a meeting of the House and Senate Democratic leadership. Participants say that Manatt sets the agenda and moves the discussion along, usually on what one called "safe topics," like the plans for the mini-convention or the next big fund-raiser.

"He comes in with his flip-charts, just like a Harvard MBA," said one participant, "and that's unusual enough up here, so they all listen."

Manatt has had some failures outside the policy area. His effort to shorten the presidential campaign season was overwhelmed by the ambitions of contenders to get a head start and of individual states to get to the head of the line in staging primaries, caucuses and straw votes.

The strength of his chairmanship, almost all those who have watched him agree, has been in the basics: fund-raising and grass-roots party-building. And he has been helped mightily in both areas by the alarm traditional Democratic constituencies have felt at some Reagan policies.

Organized labor ended an eight-year estrangement even as he took over, gaining 15 seats on the Democratic National Committee and contributing about 20 percent of its budget. Manatt pushed the party into vocal opposition to Reagan's sale of Airborne Warning and Control System (AWACS) planes to Saudi Arabia, reaping a reward from revived Jewish support.

His biggest potential fund-raising success is in direct mail, where aides say the DNC has gone from 25,000 contributors to 230,000. The start-up costs of that drive mean that Republicans have continued during the last two years to increase their lead in both receipts and expenditures. But as time goes on, aides say, the expanded contributor base will put the Democrats back into a more competitive position.

Similarly, in organizing efforts: Manatt took one small state, New Mexico, and used it as a laboratory for a coordinated voter registration, targeting and turnout effort, using national funds to pay consultant Matt Reese to pull together the efforts of individual campaigns.

The payoff was spectacular: Democrats held the governorship against a serious challenge, captured a Senate seat and a newly created House district, and other offices. Next year, Manatt says, the program will be expanded to as many as 10 states.

Probably the biggest compliment to Manatt's work came this week from the new Republican national chairman, Frank J. Fahrenkopf Jr. Manatt had come to office in 1981 saying publicly that he wanted to emulate what Bill Brock did at the RNC in the period from 1977 though 1980. Fahrenkopf said Thursday that his goal was to catch up to Manatt. "We made a mistake in reading our press reviews," he said, "and thinking that we were so technologically advanced over the Democrats they'd never catch up . . . . We have to get back to the basics . . . ."

Manatt is moving into a position where he has goodies to hand out. He will have the controlling voice in the decision where the Democrats meet and in the arrangements for the convention, giving him leverage with the aspirants.

He told the state chairmen Thursday night, "The next two years will be more fun." For Manatt, they probably will be.