It could have gotten right ugly, there in the Caucus Room of the Russell Building. Them vs. Us, Left vs. Right, Rep. Larry Patton McDonald (D-Ga.) personally asking Jeff Stein, Washington editor of the Progressive magazine, to leave a reception for McDonald and the advisory board of his Western Goals Foundation last night.

McDonald would explain later: "If you had a reception of B'nai B'rith and an American Nazi showed up, would you be surprised to see him ejected?"

"I was invited to this reception," said Stein, prior to ejection. He held up an invitation for anyone who wanted to see it, which nobody did, especially McDonald, who strode out of the Caucus Room to enlist the aid of two policemen in ejecting Stein.

Stein, a Bronze Star winner in Vietnam, waited bemusedly for them to come through the crowd.

"I want to talk to my former commanding officer in Army intelligence," said Stein with ironic plaintiveness, and introduced himself to Gen. Dan Graham, former head of the Defense Intelligence Agency.

The crowd of several hundred was full of retired generals: Gens. Raymond Davis and Lewis Walt of the Marines, Gen. John Singlaub, who left the Army after bucking President Carter on the question of removing U.S. troops from Korea, and Gen. George Patton, wandering about with a small cigar and a hard stare. Rebuilding Western civilization (one of many foundation goals) being too important to be left to the generals, there were also in attendance conservative lights such as Reps. Bob Stump (D-Ariz.) and Phil Crane (R-Ill.), Sen. Paul Laxalt (R-Nev.), Sam Francis of the Heritage Foundation and Howard Phillips of the Conservative Caucus, along with a string quartet, a bartender handing out champagne to drinkers and water to nondrinkers, and, of course, Stein.

"You're not on the list; I made it up myself," Stein was told by aide Linda Guell who, flanked by two Capitol policemen, had arrived at last.

"I have an invitation. I'm on your mailing list," Stein pleaded quietly.

"He is a congressman," said officer M.A. Kennedy.

"You're not on the list," said Guell, who works part time for McDonald in the House and part time at the Western Goals Foundation.

"I have an invit . . ."

"Let's step outside and talk about it," suggested Police Lt. R.C. Garson.

"You're a congressman and you're acting as a door usher?" Stein asked McDonald, who stood serene behind the jeweled lapel pin of the John Birch Society.

Said Lt. Garson to no one in particular: "If a person is not invited, he can be arrested for unlawful entry."

Stein walked unassisted from the field, waving to an onlooker and saying, "The power of ideas!"

Minutes later, McDonald was glad to explain everything. It wasn't the invitation question that seemed to bother him about Stein as much as the fact that "he's sort of a principal with IPS" (Institute for Policy Studies, a left-wing think tank where Stein later said he worked for four months on two projects, the last one in 1978). Said McDonald: "Who're we kidding, seriously? We know where we stand, we know where they stand."

Across the room Gen. Patton, asked where the Western Goals Foundation stands, eyed his questioner as if he were something he'd just picked out of his teeth, and yanked from his pants pocket a pamphlet urging the rebuilding of Western civilization, and advertising books such as "Red Tide Rising in the Carolinas."

"Give that back," he said, later relenting when he recalled he had another one at home.

Over by the string quartet, which was playing "Paragon Rag," Leszek Ochota, who described himself as an allergy specialist and psychiatrist with the Food and Drug Administration, offered an analysis of the crowd.

Ochota, a foundation member, a former John Bircher and "a right-wing Polish conservative," said, with a touch of Old-World accent, "This organization is not so right-wing. Don't get excited about this. If you take some of these people, you will see rich American housewives who come to these things for the parties. All of these people, they're the haves, you never meet a single one poor. I would say 60 percent of people here are reactionists, you know Newton's Third Law of equal and opposite reaction? The younger ones, 30-40 percent, have a program."

It was neither all politics nor rich people, however. There was the usual crowd of Capitol Hill interns who wandered in lured by crab claws and champagne, and thoughts, no doubt, of a place where "things go glimmering," as F. Scott Fitzgerald once said. The trick, said Elizabeth Tibbetts, of the Massachusetts delegation, is to read the literature at the door in case someone wants to talk to you. Then again, Ken Marx, an intern in the office of Rep. Stewart McKinney (R-Conn.), seemed content to sip the champagne, listen to someone ask him if he knew what Western Goals was all about, and answer: "No."

Back in the center of the floor, McDonald was talking about his hopes to reestablish a House Internal Security Committee and saying: "Let's face it, dealing in an area of subversion and terrorism is a nasty one."

"This is a real cross section of the conservative community," said Phil Kent, an aide to Sen. Strom Thurmond (R-S.C.), and wearer of a button reading: "ANOTHER FRIEND OF JIM WATT," referring to the secretary of the interior. He added: "I went in this room two nights ago to a Sierra Club reception with this button on. You should have seen their faces. I loved it, you can quote me."

And after it was all over, Jeff Stein offered: "I was just on my way to the movies when I thought I'd stop in there and see what was going on."