The storefront on Haight looks like any other, except that the signs in the window are not announcing bargains in natural food or any of the other favorite consumables of the local youth culture. Instead they proclaim: "Stop Ronald Reagan. Stop the Moral Majority."

Inside, Rich Hayes and Tessa Rouverol were busy Monday afternoon putting into their Texas Instruments computer the latest of more than 14,000 names of new Democratic registrants turned in to their center since the pre-primary registration drive began about five weeks ago.

On the wall, green, red, yellow and blue pins marked the shopping centers and busy intersections assigned to the volunteers from the League of Conservation Voters, the Democratic-Socialist Alliance, the Nuclear Freeze Voter PAC, the organizations of black, Hispanic, Chinese and gay Democrats, and the random out-of-work individuals recruited by want ads promising $30 to $40 for an afternoon's work.

Each of the 14,511 Democratic registrations among the 16,626 signed cards is redeemable for a 70-cent payment to the organization or individual credited with turning it in to the center.

Statewide, said California Democratic Chairman Nancy Pelossi, well over 150,000 names had been collected in the seven registration centers when registration for the June 8 primary closed Monday.

That is a small but significant start on the goal of enlisting 1 million new Democrats by November in a party-registration drive that is both the symbol and the foundation of a major effort to turn the political tide in the nation's largest state.

Party leaders see the configuration of issues and circumstances this year as a rare opportunity to unite the elements of the Democratic coalition for a top-to-bottom sweep in the November elections.

As Pelossi and the Democratic registration director, Assemblywoman Maxine Waters of Los Angeles, readily concede, the California Democrats have no place to go but up, after suffering through a case of near-terminal neglect in 1980.

Jimmy Carter lost the state by 1.5 million votes, after a minimal campaign effort, and Democrats also dropped three House seats, in part, they say, because Carter conceded to Californian Ronald Reagan before the state's polls had closed.

Under the blight of the Carter candidacy, California Democrats were outregistered by the Republicans in 1980 and saw their share of the registration drop below 53 percent for the first time in anyone's memory.

Waters said that if the drive that will resume this summer and peak in the fall hits 750,000 of its 1 million goal, the percentage will jump above the 56 percent level where, she said, "Democrats can normally be assured of statewide victory."

The Republicans plan a post-primary registration drive of their own, but surveys show that 60 percent of the 4.2 million unregistered adults in the state are Democrats. By choosing registration sites carefully, as in San Francisco, the Democrats can get as much as an 87 percent return on their investment. As Waters said, "We're not paying for switch-hitters."

As impressive as the scale of the effort is the coordination of the drive.

It is being funded through the party by six-figure contributions from the prospective Senate nominee, retiring Gov. Edmund G. (Jerry) Brown Jr., the prospective gubernatorial nominee, Los Angeles Mayor Tom Bradley, and the senate and assembly Democratic caucuses. Portions of a $40,000 pledge from the Democratic National Committee and contributions from labor unions also will go into the fund, Waters said.

With the bounty for Democratic registrations set at $1 a head in some parts of the state, the drive is budgeted at $1 million.

All this is a far cry from the normal do-it-yourself approach of California Democratic candidates. It reflects the unusual luxury Democrats enjoy in knowing well in advance the identity of their nominees. Brown and Bradley both have nominal opposition in the primary, but neither is seriously threatened.

The Republicans, by contrast, have close, hard-fought battles under way for their senatorial and gubernatorial nominations.

It also reflects the belief, expressed by Assembly Speaker Willie Brown, one of the spark plugs of the party-building effort, that "Democrats have a golden opportunity for a top-to-bottom victory in California this year."

Brown pushed through the legislature a highly partisan redistricting plan, created by Rep. Phillip Burton (D-Calif.), designed to boost the Democrats from 22 to 27 House seats and expand their majorities in the senate and assembly.

Republicans are backing, and will probably win, a June 8 referendum invalidating the "Burton gerrymander," but the courts have ruled already that it will stay in effect for this year's election, no matter what happens in the referendum.

As the signs on the Haight headquarters suggest, Democrats say they believe the polls showing that Reagan's popularity is declining rapidly in his home state and that they think they can target public resentment over his social and economic policies.

They also say they believe that, if the registration drive meets its goals, a number of factors could boost the turnout of Democratic constituencies in November.

The black community has the prospect of seeing Bradley become the nation's first black governor since Reconstruction. He has been leading in all published polls against the rivals for the Republican nomination, Lt. Gov. Mike Curb and Attorney General George Deukmejian.

The Hispanic community, where pre-primary registration has been boosted by the challenge to Bradley from Brown cabinet aide Mario Obledo, will have the opportunity to elect at least two more congressmen in the reapportionment. An additional lure will be the confirmation vote on Cruz Reynoso, named by Jerry Brown as the first Hispanic justice on the state supreme court.

A referendum on the nuclear freeze has qualified for the November ballot and is being boosted by disarmament groups around the state. Another likely winner, according to the polls, is an initiative put- ting strict controls on handguns, for which petition signatures are still being gathered.

Some Republican strategists say they think this collection of liberal candidates and issues--focusing on the always controversial personality of Jerry Brown--will alienate conservative Democrats in the Central Valley and create a backlash GOP candidates can exploit.

But Pelossi, Waters and the two Browns see it, in Pelossi's words, as "a once-in-a-generation chance" to mobilize their party's diverse coalition in a way that never happened during the Carter years.