For the most recent important function in Statuary Hall in the Capitol, a July 8 bicentennial luncheon for Britain's visiting Queen Elizabeth, a chamber group played Bach an improvised fountain splashed, and white-gloved waiters circulated among the titled British guests and congressional leaders.

Yesterday, for the opening of the 95th Congress, the scene in Statuary Hall, site of the original chamber of the House of Representatives, was pure Americana.

Over 500 Boston-area friends of the new House Speaker, Thomas P. (Tip) O'Neill, packed into folding chairs set up in the hall to watch his swearing-in on closed-circuit television. With names such as Sullivan and O'Rourke and Malloy, they cheered as if it was a prizefight when O'Neill was nominated and booed when his pro forma opposition, Minority Leader John J. Rhodes (R-Ariz.), was named.

Walter Sullivan, a Cambridge city council member and long-time friend of O'Neill, said the group was comprised of local public officials, campaign workers, campaign contributors, Massachusetts State House lobbyists, and "a lot of priests."

"And Tip's bookie, don't forget Tip's bookie," a helpful bystander yelled.

Sullivan said they weren't invited, they just decided to come because O'Neill was "a good friend and a real Irisher." They chartered three planes and paid their own way, he said. Though O'Neill was busy with official opening ceremonies and meetings all day, he would be all theirs in the evening when they threw a big hotel reception for him.

Similar scenes were repeated all over the Hill yesterday, as constituents, friends and contributors showed up at Senate and House office parties and dozens of receptions to cheer the man they backed, particularly if he was newly elected.

Few got to see the actual swearing-in. There are only 624 seats in The House public galleries, so it was only one or two seats to a member, though O'Neill got nine. Senators did somewhat better.

The scenes in the two chambers reflected their distinct differences. It was grand opera in the Senate, grand ol' opry in the House.

The Senate was organized, dignified, restrained. Senators were sworn in in small groups accompanied by their state colleagues if they were new. The applause was polite.

In the House, which believes it is "the people's body," it was a raucous din. As if testifying to the recent enormous turnover (half the House has been elected since 1970) and the youthfulness of its members, the House floor was packed with children.

O'Neill's acceptance speech was punctuated with the babbling of babies. When the three-month-old son of Max Baucus (D-Mont.), as yet unnamed, began to cry, Baucus expertly plucked a bottle from his pocket and stuck it in his mouth, then pulled out a diaper to burp the baby.

Two of the three red-headed children of 31-year-old John Cavanaugh, a newly elected Democrat from Nebraska, slid across a table, white Cavanaugh pushed a third up and down the aisle in a stroller.

Yvonne Burke (D-Calif.), the first member to have a baby while serving in the House, held her toddler in her lap, beside the House's first husband-and-wife team, Andy Jacobs (D-Ind.) and Martha Keys (D-Kans.).

But age was served, too. The last speaker from Boston, retired 85-year-old John McCormack, returned to see a reinstatement of the Boston-Austin axis. McCormack had served as Texan Sam Rayburn's Majority Leader; now Texan Jim Wright would serve as O'Neill's.

Just retired Speaker Carl Albert was there, too, and along with McCormack escorted O'Neill to the Speakers platform. Albert's office across the hall from the chamber now stands bare; he was taken everything, from desk to pictures, to create a replica of his office at the University of Oklahoma.

While it was a day of ceremony and tradition, for at least one member a little reality, a specter of things to come intruded too.

Peter Kostmayer, a 30-year-old freshman Democrat from Pennsylvania, had sent out engraved invitations to his Bucks County constituents for his office-warming party here today. The only problem: he didn't have an office yet.

He was assigned Suite 1017 in the Longworth Office Building. But reelected Rep. Marilyn Lloyd (D-Tenn.) has that office now and isn't moving until her new office is vacated. And that could take weeks, because a number of retiring congressmen haven't cleared out yet. Kostmayer hastily moved his reception to the nearby Democratic Club.

"It bothers me somewhat not having an office," Kostmayer said. "But the thing I really care about is my committee assignment. I may get a bad deal on that, too."

Thus Kostmayer got an early introduction to an old truth. Seniority still exists, and while some things have changed, a lot remains the same in the halls of Congress.