Walter Mondale, looking back on 25 years in Washington as senator, vice president and citizen, said, "We knew what we were doing and we remembered what we did. We told the truth and obeyed the law. That's everything in a democracy."

Last night, at a going-away party that sounded more like a coming-out-for-election rally, Mondale looked at a quorum of his old Democratic congressional colleagues and supporters and told them, "We believed in social justice, and passed legislation to accomplish it. We believed in civil rights and started a revolution." And, he said, the old friends before him believed in environmental "decency," strength for peace, arms control and international understanding -- and did something about them.

The party, in the Gold Room of the Rayburn Building, was given by "Friends of Walter and Joan Mondale": Rep. Bill Alexander (Ark.), former senator Thomas Eagleton (Mo.), Sen. Daniel Inouye (Hawaii), Sen. Pat Leahy (Vt.), Rep. Charles Rangel (N.Y.) and fundraisers Bill Cotty and Nate Landow. The government in exile was so tightly packed that there was hardly room to raise a glass or one of the elaborate whipped-cream pastries.

The crowd, called to attention by a two-finger whistle by Rangel, replied to Mondale's fiery speech with a voice vote that was a fierce acclamation.

The band played the old Democratic marching song, "Happy Days Are Here Again." And Fritz Mondale confided to the crowd that Alexander had told him the party was a success because "they're all delighted to see you leave."

The crowd did seem happy the former vice president and his wife are moving back to Minnesota on Aug. 20. But they made it plain that's because they expect him back, in the Senate.

Sen. Ted Kennedy (D-Mass.) stopped long enough to tell another party-goer that he for one "would like to see a rematch" between Mondale and President Reagan.

Mondale, commenting on Kennedy's remark, said, "I think a lot of people, looking at this mess, might agree. Well, you know, in every speech I made during the presidential campaign, I said Reagan was 'out of touch, uninformed and not in charge.' "

The party was across the hall from the site of the Iran-contra hearings, which ended their open sessions Monday.

Inouye, chairman of the Senate Select Committee that held the hearings with its House counterpart, admitted between bites that he'd been on television more during the hearings "than any time in my whole political career before this. I think I'd been on maybe four times before. Now I'm prepared to fade away." Someone said, "Surely not!" And Inouye grinned and replied, "Look for the next scandal."

Later, in one of the mini-speeches, Inouye said that during the hearings, "I've been asking how it would have been if Mondale had been in the White House. And I know his reaction would have been one we would've been proud of, where integrity, sanity and honesty were the coin of the realm. The United States certainly missed the boat in that election."

House Select Committee member Rep. Dante B. Fascell (D-Fla.), resisting the temptations of the cheese stand, pointed out that "the hearings aren't over yet. The staff will be taking depositions and writing reports for a month or so. Meanwhile, I'll be back home campaigning."

Presidential hopeful Sen. Joseph R. Biden (D-Del.), dashing out the door with his wife to catch a train home, said he'd had good advice from Mondale on running for president, but "I'm not the only one."

Joan Mondale, famous for her total recall of names and places where she saw people last, shook hands and recalled old times with every guest. She said she planned to start packing in the basement today after she played a last game of tennis with an old friend. Though they are keeping their Washington house, she said they have sold their house on the lake back home and "We've bought a new house in Minneapolis, where Fritz is going to practice law."

And Mondale invited them all to visit. "We have plenty of hotel rooms there, especially in February.