There were Republicans as far as you could see, which admittedly wasn't that far in a room made murky by atmospheric lighting and dark Washington lawyer outfits. But oh, it was jolly. "Happy days are here again," one of the chortling attorneys said.

The occasion for last night's mirth at the International Club was first off, Ronald Reagan, and second, a reception to celebrate the new Washington law office of Milbank, Tweed, Hadley & McCloy. This is a conservative Wall Street firm that has 220 lawyers, a new star attraction in Elliot Richardson, a few ties to the incoming administration, and a lot of competition.

That's because Milbank, Tweed, etc., is yet another law firm that has opened a branch office here, the clever thing to do if you want to hang on to your big corporate clients who need Washington specialists.Last night, Milbank, Tweed's reception would have been just another opening office party but for Richardson and all the Washington Republicans who came parading out of big cars and obscurity.

In fact: Considering the Republicans, the Milbank lawyers, a new administration and the scotch, the whole scene made for a wonderful little glimpse of transition-time Washington. Or, whom do we know on the Hill who knows Bob who knows someone at Justice who was an undersecretary of . . .?

"Jim Baker's doing very well, isn't he?" somebody in the long stream of law firm congratulants said to Richardson, who once spent more time switching Cabinet jobs than a lawyer spends at lunch.

"Oh, yes," replied Richardson, referring to Baker, the president-elect's new chief of staff."And that's good for us, isn't it?" To follow this, you have to know that Baker was once undersecretary of Commerce to Richardson, who was secretary of Commerce. For one year. But certainly, vital connections between Washington law firms and the existing power structure have been made in a lot less time.

As it happens, Milbank, Tweed is not among those Washington firms currently being touted as one to rise with the new administration. A better bet, local lawyers say, is Gibson, Dunn & Crutcher, the Los Angeles-based firm of William French Smith, Reagan's lawyer and top possibility for attorney general. Or, Latham Watkins & Hills, as in Rod and Carla Hills, establishment Republicans.

Still, the McCloy in Milbank, Tweed, Hadley & McCloy is John McCloy, a former ambassador, Chase Manhattan board chairman and member of FDR's administration. Now he's on Reagan's transition team.

And then there's Richardson, who last night said hello to people like former senators William Fulbright and John Sherman Cooper, Tommy Corcoran, Anna Chennault and FBI Director William Webster. Webster's job status in the Reagan administration?

"Now that's an interesting question," he replied. "I haven't packed any bags."

Richardson, who had at least five other law firm offers after he left his latest job as ambassador-at-large, wasn't exactly expansive either. Particularly about his new salary.

"Heavens, I'm not going to answer that," he said.