When Democratic presidential hopeful Gary Hart went through the receiving line at the Congressional Hispanic Caucus last night, he counseled Hispanic Rep. Bill Richardson (D-N.M.) to stay uncommitted. When Democratic front-runner Walter Mondale arrived, he told Richardson, "I'm going to need you," the congressman recalled.

"It's tough," said Richardson, who was elected last November. "They all campaigned for me. Mondale was in New Mexico a whole day for me. Hart was there a whole day. It feels good to be courted. But at the same time, I wish there were easier choices in politics."

Fortunately, Richardson, in tuxedo and sporting a white carnation, can make his decision another day. Last night at the Washington Hilton Hotel, he and eight of his fellow Hispanic Caucus members were having their day in the power spotlight. For though this dinner for 1,200 (each of whom paid $150) may have been "family" and largely Hispanic, according to Rep. Robert Garcia (D-N.Y.), the caucus chairman, the dinner was a must on the crowded schedule of the political powers.

Hart and Mondale were there. So was Annie Glenn, in the place of her husband John. Also there were Charles Manatt, the Democratic National Committee chairman, Julian Dixon, chairman of the Congressional Black Caucus, and, of course, House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.), who made a keynote address that was scathingly anti-Reagan and won him a standing ovation.

"This is really the kickoff to the 1984 campaign for us," said Mike Steed, the DNC's national director.

The nation's Hispanic population lags in voter registration, something that didn't escape the attention of the Democrats here. "We're already with the Democratic Party," said Polly Baca Barragan, DNC vice chair and a Colorado state senator. "The Democratic Party is the only mechanism that responds by letting us elect members to Congress."

The lone Republican in the Hispanic Caucus is Manuel Lujan Jr. from New Mexico. "Democrats tend to divide us and say, 'You poor unfortunate things,' " Luhan said. " 'You were born Hispanic and you can't help it, but we have a government program that will help you.' I think it's demeaning.

"But the president talks about the same things that we're all concerned about as Americans," Lujan said. "He doesn't hyphenate American--one of the things I find offensive about the Democratic candidates."

The Democratic candidates, though, were besieged with attention. Mondale virtually stood at the table where he and his wife, Joan, had been seated, and let the crowd work him. "This is exciting," said Mondale, who said of the Hispanic community: "They're voting, they're getting organized . . . If you look at the new leaders . . . they're overwhelmingly Democratic."

Gary Hart said he was there because "I just wanted to come and say hi to a lot of old friends . . . It's a chance to see an awful lot of people from all around the country . . ."

John Glenn couldn't make it because "he's off in Connecticut. He's raising money," said Annie Glenn with a chuckle. Garcia got a little carried away with his introductions during dinner and said of her: "Another presidential candidate, from the state of Ohio, a magnificent astronaut, a person who has made his mark in the Senate, Mrs. John Glenn."

Early on before dinner, Lujan had worried that O'Neill would deliver a partisan speech and had said that this wasn't the place for it.

Sure enough, O'Neill prefaced his remarks by saying, "I'm extremely partisan--a jovial fellow, but partisan."