"We were'nt sure, " said James E. Kelly of Fort Wayne, Ind., not even trying to hide a mischievous grin, "whether it was an engagement announcement by Ethel and Birch or an involvement announcement by Birch and Teddy."

It turned out to be neither last night. Instead, it was a fund-raiser for an embattled liberal senator with the price of admission entitling the bearer to one close-up look inside Hickory Hill, one handshake from Ethel Kennedy, six growls or wags from the Kennedy dogs and one speech from one Kennedy senator.

The gathering had these and other elements of what may be becoming the newest Washington institution: the Hickory Hill Rescue Squad. It includes:

The fighting senator: Last night he was Birch Bayh, a three-term Senate veteran and one of a half dozen or so Democrats whom right-wingers have targeted on hit lists for political annihilation in 1980.

"They've started sending letters out of state to raise money to spend back in Indiana," Bayh said. "They're a bunch of haters.And they're talking about spending $200,000 on my race."

The last embattled liberal feted at Hickory Hill was Iowa's Sen. John Culver last spring, but then 100 Iowans paid only $100 per person. Inflation?

The take: Some 150 supporters paying $1,000 per person came from Indiana and Ohio as well as the District making it one of the fatter fund-raisers of the fall season.

"Carter came to Indiana for a Democratic Party fund-raiser last spring and raised $220,000 from 3,500 people," said Claude Magnuson, state party treasurer. "If you can have a little party like this for $100,000 for 150 or so people, it's a hell of a lot better." The Hickory Hill tour: The throng started arriving at 6:30 p.m. and didn't stop coming, fanning throughout the elegantly appointed home of the late Robert F. Kennedy. There were Bayh supporters from Indiana, lobbyists from Capitol Hill and even a union president from Akron, Ohio, (United Rubber Workers International President Peter Bommerito). They inspected the paintings, the photographs, the rugs and upholstery, and in the crush, one of them found himself on fire. "I thought, 'Boy, is it hot in here'," said Claude Magnuson. "That's the trouble when you concentrate on your conversation too much." Several candles were burning in holders around the living room and Magnuson had backed up against one of them.

Ethel Kennedy, who kept clutching at the neckline of her green chiffon dress and worrying that it was too low, said one thing she didn't worry about was what might happen to her house when it was over-run by curious crowds.

"So much garbage goes on here every day," she said, motioning to a couple of young Kennedys passing by.

The Ethel Kennedy handshake and chat: "You saw him three times? You lucky dog, how did you do it?" she said shaking hands with Phil Leonard, COPE director of the United Rubber Workers, who had told her about seeing the pope last week.

The children's hour: There were four Kennedy children -- Rory, 10; Doug, 12; Max, 14; and Christopher, 16. Rory's curtsey was shakey, but otherwise she showed promise of being a successful political campaigner. The boys, acting conspiratorial, were "up to no good -- I can tell," said their mother. She was not too far wrong because almost the next instant there appeared on Evan Bayh's lapel a hastily pencilled name tag reading "I am ugly." Evan, who is not ugly, is a second year law student at the University of Virginia and a classmate of Robert F. Kennedy Jr.

The pets: Last night six were present, all dogs tracking in mud.

The speech from the Kennedy senator: When Sen. Edward M. Kennedy made his appearance near the end of the party, it was like a shot of political adrenalin to the crowd. He moved in with a ready handshake and an easy smile, working the crowd like the party was for him rather than Bayh.

In the living room, Kennedy summed up Byah's significance in the Senate and especially on the judiciary commitee where "everyone . . . knows the Supreme Court is better because of the great work he did."

Their relationship, he said, went back to the John Kennedy presidency when he campaigned in Indiana for Bayh, recognizing Bayh's "enormous potential for our party." Beyond that was their personal experience of the 1964 plane crash when Bayh dragged Kennedy out of the debris, "and perhaps saved my life."

And later, as Kennedy moved through the mob, pressing the flesh and being pressed, he talked about the significance for him of the Florida caucus on Saturday when he and President Carter face each other in a state-wide straw vote.

"I'm very grateful for the support of those who have expressed interest in me in Florida, but of course I'm not a candidate. The only fair test will be if I were a candidate and running in an election," Kennedy said.

He said he expected the president to do "extremely well" there since it is a neighboring state of Georgia. And he said he didn't think it was really "reflective of working members of our party because of the complexities of the selection process. I think the first contest will be Iowa and New Hampshire."

The curtain call: Nobody could get enough pictures of Bayh, Ethel Kennedy and Ted. And when the senator finally made it to the front door, he found three of Mrs. Kennedy's employes lying in wait. He rose to the occasion, beaming his toothiest smile and towering over Gino and Maria Teresa Vistosi and Tita Santana while the moment was recorded on film. Maria Vistosi was ecstatic, but Santana was gloating. She's a nine-year domestic veteran of the Kenndy household. "I get my picture with him all the time," she said, grinning.