There was a shocked silence in a corner of the Maison Blanche yesterday after Midge Costanza told a few friends, "I'll be moving back to New York in two or three weeks, and I'm very seriously considering taking Gov. Carey's job."

After a few tantative questions, it developed that Costanza is not thinking of running for governor of New York but of taking a job that the governor has offered her. "He wants me to act as liaison between the State of New York and the federal government. It looks interesting, and I want to move back anyway to maintain my legal residence in New York. I'm a member of the Democratic National Committee from that state, and I suppose I should live there in case someone asks."

Costanza was one of about 50 guests at an early evening cocktail reception for Hollywood scriptwriter Colin Higgins, author of such screenplays as "Harold and Maude," "Silverstreak" and "Foul Play," which he also directed.

"It's funny," said attorney Lester Hyman, one of the guests. "When a Hollywood personality has a party in Washington, the politicians flock to it, and when a politician has a party in Los Angeles, the film people flock to it."

The politicians who flocked to exchange greetings and bend an elbow with Higgins yesterday were mostly new-breed members of Congress, including Sen. William Cohen (R-Me.) and Reps. Pat Schroeder (D-Colo.), Don Edwards (D-Calif.), Robert Carr (D-Mich.), Timothy Wirth (D.-Colo.) and Don Bonker (D.-Wash.) Also present was Gov. William Clinton of Arkansas, who looks a little bit like a freshman full back on a college football team.

Gov. Clinton stayed only briefly. "He has to give a speech to the Arkansas Chamber of Commerce at the Capital Hilton in 20 minutes," explained a friend. Why was the Arkansas Chamber of Commerce meeting in Washington? "To see the big city, get a little drunk and have a good time without anybody watching," explained someone in the crowd.

From the governor's conversation with an old buddy named Mike Driver, it turned out that the party was also a reunion of sorts. "We were just reminiscing," he said, "and looking at where we have gone in the last few years. We all worked together on the Vietnam moratorium; now, I'm the governor of Arkansas, Mike is representing an oil company, and David is a Hollywood mogul."

"David" was David Mixner, partner with Peter Scott in a company called Mixner/Scott, which was the host of the party.

"Mixner/Scott? The represent one branch of show business to another," said Rep. Carr. Scott explained more fully: "We represent the film industry in relations with the federal government and do some political consulting in California. We're also doing some work for Jerry Brown."

Costanza, who has been working as a consultant for the company, gave some inside information on her consultations: "In California, I told tham Jerry Brown could never be president. With his sense of austerity, the only place he could live is Amy's tree house, and it only sleeps one."

She had some double-edged words, too, for the incumbent president: "He has a great sense of humor. I remember I used to go in and tell him, 'Hey'" (punching a bystander lightly on the shoulder to indicate her treatment of the president), "what a great straight man you were for me today."

Then she put on a southern accent for the president's line: "What have y'all been sayin' about me now?" And back to the Costanza voice: "I told some people, if you went to all the trouble of being born again, why did you come back as your same old self? You can use that line if you want to," and another light punch on the shoulder ended the conversation.

Higgins, still a little groggy from a red-eye flight from California, said he came to Washington "just to hang around for a few days-I've just finished writing 'The End' on a script for Paramount and I'm taking some rare vacation time." But he added that he will be going to see a press conference today and that he is thinking of doing "a sort of 'Nashville' on Washington, D.C.-still feeling my way around, wondering what kinds of characters to use and how to get them into the action." He will find that a lot of people in Washington share that final wonderment. CAPTION: Picture, Colin Higgins and Midge Costanza, by Joe Heiberger-The Washington Post.