An impressive chunk of the political establishment was out rollicking and toasting last night for two departing congressional institutions -- Rep. John Rhodes (R-Ariz.) and Rep. Richard Bolling (D-Mo.). After sitting on opposite sides of the mighty House chamber for three decades, you'd think the legislators would be saddened.

Not so. Goodbyes seem to take on a certain elegance in Washington when they're not linked with defeat.

"Why would I be sad? Not one bit," boomed Bolling between familiar congressional hand-pumping and backslapping in the Rayburn building's courtyard. "I'm about to embark on a new career of talking, writing and thinking. I'm gonna have a good time . . ." Pin stripes and private jokes prevailed.

"There's an old saying," explained Rhodes, across town at the Washington Hilton, as flashes exploded in his face. " 'Get off the stage when the audience is yelling for more.' It's time to go!" Black ties and jeweled necklines dominated.

As per Washington tradition, interfering roll calls and political banter gave both parties the frenzied touch usually linked with raucous conventions. At the Capitol, it was a vote on food stamps that sent everybody scurrying at 6:15. At the Hilton, it was the threat of a vote on the train strike.

"Are you calling us back for a vote -- or can we stay here at the party?" asked Sen. Dennis DeConcini (D-Ariz.) as Senate Majority Leader Howard Baker (R-Tenn.) tried desperately to get out the Hilton's front door while everyone else plowed in. "Don't worry, I'll call down here," said Baker. "There'll be plenty of time."

"This is Senator Goldwater and I'm concerned about a vote," said Barry (R-Ariz.) into a pay phone. "Senator Baker left. Be sure and call . . ."

No one seemed to call through the length of the four-hour Rhodes affair. And Baker was the only one to leave. So the talk of the forthcoming congressional recess, Lebanon and John Rhodes marched on.

First a word or three from Sen. Robert Dole (R-Kan.) on Rhodes and others. He brought down the house. So to speak.

* "If there are any skeletons in John Rhodes' closet, they're probably the bones of old reporters trying to find something wrong in John's life. Or interesting."

* "Tip O'Neill's luck is not so good these days. It's so bad that on St. Patrick's Day he found out he was Italian."

* "John is a low-key guy . . . He's so low-key that he had to tell Senator Sam Hayakawa to slow down."

"Remember when John Rhodes, Mel Laird and Jerry Ford used to have Wednesday morning prayer meetings? . . . Can you imagine them praying together? . . . It was the only day of the week God fell asleep."

Later, in a serious moment, Dole commented that he supported the president's decision to send Marines into Lebanon. "We have interests that we have to protect," said Dole. "I hope the Israelis do the right thing and leave."

"I want to support the president but there is a lack of clarity about the situation that concerns me," said Sen. John Warner (R-Va.). Warner said he had just come from a State Department meeting on the Lebanese issue. "I'm worried about the safety of the Marines and where they are going to locate."

The Rhodes crowd could have been mistaken for who's who in Dun & Bradstreet. Ford Motor Co., Bendix, Martin Marietta, United Technolgies, U. S. Steel, Eastern Airlines, Burlington Industries and Philip Morris were among those represented at the $125-a-plate dinner.

"This is a political event," said Nancy Reynolds, Reagan insider and Bendix vice president. "John has been a friend to all of us. He's a well-respected legislator."

House Speaker Tip O'Neill managed to change into his tux between the 5 p.m. Bolling cocktails and the 7 p.m. Rhodes dinner, and make both events.

"Gee, he's been my strong arm," O'Neill said of his good friend Bolling. "He's the most able guy to hit Congress in the last 30 years. It's a terrible loss. Not only to Congress but to me."

In the end, Bolling got a wooden goodbye plaque from his friends before they went off to vote. And Rhodes got a surprise taped goodbye message from President Reagan and the key to the Capitol doors. In case he wants to come back.

"A lot of Washington dust has accumulated on my feet in the last 30 years," said Rhodes. "I'm not going to even try to get it all off." He adjusted his ruby rose boutonniere, winked and walked off. There was a whole lot more partying to do.