Help us," prayed the rabbi at a recent political dinner, "to recognize the incongruities of this day." The incongruity of the event was apparent without any inspiration from the Lord.

The occasion was the announcement of the candidacy of a Democrat running for his party's nomination in California's 44th Assembly District, the kind of announcement usually made in a neighborhood hall by a candidate in dire need of campaign funds and publicity.

But this was Tom Hayden's dinner. Held at the Century Plaza Hotel where President Reagan often stays, it glittered with Hollywood stars. It drew the attention of nearly every newspaper and television and radio station in Los Angeles. And it netted $100,000.

Of course, other local candidates aren't married to Jane Fonda.

And other local candidates aren't Tom Hayden. Hayden has been an object of media attention for almost two decades, since he came to national attention as a leader of the radical student movement in the 1960s. That helps by drawing press attention and gives him almost total name identification among voters in his district. It hurts, too.

Hayden describes the press coverage like this: " 'Onetime radical trying to get into politics.' It's quite bizarre, it makes me feel about 23. People are surprised to hear that I'm 42 years old. I got frozen in terms of images."

In 1976 Hayden challenged then-Sen. John V. Tunney in the Democratic primary and did well enough that some Democrats blamed him for the loss of the seat to S.I. Hayakawa in the general election. Tunney is campaign co-chairman for one of Hayden's opponents in the assembly race.

After the 1976 election Hayden founded the Campaign for Economic Democracy (CED), a grass-roots organization active in local elections and such issues as rent control and solar energy. California Assembly Speaker Willie L. Brown said that "members of the Democratic caucus" in the state legislature "can't seem to generate foot soldiers and people to ring doorbells and in-person power. That's unique in CED . . . . Tom Hayden may be the only person we know who we can call up and say, 'Can you give us 150 people?' "

When many voters think of Hayden they remember rioting students and that Fonda made a wartime trip to North Vietnam that resulted in accusations of treason. So, while the California Poll shows that Hayden is one of the 10 best-known politicians in the state, it also shows he is one of the least-liked.

But the Hayden that voters will meet in a major precinct-walking effort is far from being a shrill radical; he seems more vulnerable than threatening.

The 1980s Hayden talks about "a new partnership between government, business, labor, consumers and community." He worries that American business is not meeting Japanese competition and he opens a speech to the Chamber of Commerce by remarking that he is honored to be "on the agenda instead of the menu."

Hayden plans to try to raise $500,000 for the June primary, mostly from three or four major events such as the announcement dinner and a direct-mail campaign. He already has raised about $250,000.

The 44th Assembly District includes parts of Venice, West Los Angeles, Santa Monica, Pacific Palisades and Malibu, and is one of the most liberal districts in the state, despite a partly successful reapportionment effort to "de-Haydenize" it. In 1980, while Ronald Reagan was winning California by a landslide, Jimmy Carter won in the 44th Assembly District.

Many California Democrats, including Willie Brown, who isn't excited about having a media star on his turf, are leery of Hayden's image and his politics. They tried to thwart him by cutting part of Venice, one of Hayden's strongest areas, out of the district.

Hayden's announcement dinner shone with film industry luminaries, but not many Democratic Party regulars were there. Edmund G. (Pat) Brown Sr., the former California governor whose son Jerry is the current governor and is running for Hayakawa's Senate seat, is an unabashed Hayden fan but he didn't attend Hayden's dinner and won't endorse his candidacy.

"I like Tom very much and I resent all the criticism of him for things he did 15 years ago," Pat Brown said. "I think he's very able and impressive, and I'd like to help him. But my prime interest is Jerry. And if I support Tom against other Democrats, I'd be taking support away from Jerry."