There were nine speakers last night at the Sheraton Park -- all freshman members of the 96th Congress -- and understandably, a three-minute limit was imposed on their speeches.Most of them didn't quite make it, but they tried and, as a result, one-line jokes set the tone at the Washington Press Club's dinner for Congress.

Billy Carter's toilet-training was the most popular subject, with a total of five jokes. Hemorrhoids ran a close second with four, and Coca-Cola and presidential candidacies trailed not far behind.

Having heard some of the competition, Sen. Carl M. Levin (D-Mich) interrupted his own talk to say he would employ a gag writer the next time. Some of the others sounded as though they had.

Levin's best line was about his introduction to the housing problem in Washington: "I ended up my first night on one of those steam grates outside the State Department. And what's worse, I had to share it with three Iranian diplomats."

Sen. Nancy Landon Kassebaum (R-Kan.) was introduced by Marguerite H. Sullivan, president of the Washington Press Club, as having "broken an old family tradition; she got elected." Kassebaum brought down the house with the opening of her brief talk, alluding to Dorothy's statement after the tornado in "The Wizard of Oz": "Gee, Toto, I don't think wr're in Kansas anymore."

She told the 1,300-plus journalists and members of Congress at the dinner that before her election, "My title was mother; now it's senator. I'm not sure the increase in pay compensates for the loss in prestige and honor."

Earlier, during a cocktail reception before the dinner, some of the people who were not on the speakers' list got a chance to insert their own one-liners into the random babble of conversation. Eugene McCarthy recalled that "about six months after Jimmy Carter was elected, I was asked in Athens, Ga., if I thought he was a one-term president -- and I said I thought he'd make it."

President Carter, who was the object of much of the humor during the evening, had been invited but was not present. Sullivan said he "was too busy" and had sent regrets to the club orally six days before the dinner.

A White House spokesman, asked what the president was doing this evening, said that he was "at the mansion, having dinner."

The White House was represented by Hamilton Jordan, Jody Powell, Frank Moore, Stuart Eizenstat, Tim Kraft and Gerald Rafshoon. Also present but representing only herself was former White House aide Midge Costanza, who said she had been "very disappointed" at the dismissal of Bella Abzug. "I'm disappointed for the president as well," she said. Although she left the White House last year, Costanza is still living in Washington and is considering accepting a new job as liaison between the State of New York and the federal agencies.

One of the speakers offered an informal count of who is already running for the presidency: "Eight if you count Harold Stassen; 14 if you count Sen. Kennedy." Quite a few of the Republican candidates, announced and not anounced, were at the dinner, though some left early or did not show up because they were helping prepare the Republican leadership's televised reply to President Carter's State of the Union Message.

Towering above other diners as he stood shaking hands and chatting in the middle of the room was the latest announced candidate: former gov. John Connally from Texas. Asked what he was doing, he said, "Hopefully we are enlargin our constituency."

Sen. Robert Dole (R-Kans.), who has not yet made up his mind on whether he will run for president, watched Connally in action and reflected: "I called to wish him luck; now I expect him to call and wish me luck. I left my number.

Among the former presidential candidates at the dinner was Sen. George McGovern (D-S.D.). He was waiting in the line at the coat-check counter, but when he saw Connally in the same line, he turned away and went downstairs with his coat over his arm.

One freshman member of the Senate who did not speak was John Warner (R-Va.), who has been getting a fair share of media attention without giving three-minute after-dinner talks.

Before the dinner, in the room reserved for head-table guests, one fan was chatting with Elizabeth Taylor Warner and recalled: "The first time I saw you in person, you were coming out of the president's office."

"Which president? What year," the senator asked.

"President Truman, many years ago," the fan recalled. "You've come a long way since then."

One guest not as quick as usual with a joke was Ardeshir Zahedi, who said he is flying to Morocco Saturday with the shah's children, who are in this country. The shah will not come to live in the United States, he said. "He finally decided it would be better to be nearer his country."

Among the prepared speeches of the evening, the one that drew the most laughter was given by Rep. Olympia Snowe (R-Maine), who was asked: "Since you have done so much for mental health in Maine, do you see vast, new horizons in Congress?"

"In Congress," she replied, "nothing is vast -- half-vast, maybe."

She said that she sees many contrasts between Maine and the District of Columbia, "but we have one thing in common: "Neither one of us has a professional football team."

Recently, she received a letter from Robert Redford addressed to "Congressman Olympia Snowe." "My luck," she said wryly: "a letter from Robert Redford, and he doesn't even know I'm a woman."

As a woman, she also got in a crack at the president: "I'm just waiting for the day when he fires half as much enthusiasm as he does women."

She described a Washington cocktail party as an event "where everyone stands around with a cocktail in one hand and a knife in the other," but she reserved her sharpest comment for Gov. Jerry Brown of California. "There are only two things I don't like about Jerry Brown: his face."