Ronald Reagan, sounding like a prospective bridgroom about ready to pop the big question, yesterday launched an intense three-day court-ship of the Republican congressional establishment, taking special pains to seek the favor of party moderates.

The former California governor, long the darling of the party's conservative wing, won no new formal pledges of support in a carefully orchestrated series of meetings on Capitol Hill.

But Reagan, 67, drew high marks for his vigorous, if not youthful, appearance, and for taking his case for the 1980 presidential nomination to party congressional leaders.

"This is a great idea," Senate Minority Leader Howard H. Baker Jr. (R-Tenn.), a potential rival for the Republican nomination, told Reagan during one meeting. "I can't remember a Republican presidential candidate, or potential candidate, who has spent such a significant amount of time" meeting with senators.

Reagan looked and acted like a presidential candidate throughout the day. But he insisted he wasn't a candidate. Not yet, anyway.

"I realize I have a decision to make and I will make it later on," said the man who narrowly lost the 1976 nomination to Gerald R. Ford.

The jockeying for the nomination was never far away from the mind of anyone Reagan met with. When the former governor was ushered into the minority leader's office, Baker's press secretary, Ron McMahan, jokingly called the meeting "a father-and-son talk," drawing attention to the age difference between the two men. Baker is 53.

Then, McMahan sidled up to John Sears, a Reagan political strategist, and said, "He looks a little tired, doesn't he?"

Reagan, tanned and lean, didn't look tired. "He looks pretty damn good," said Sen. Malcolm Wallop (R-Wyo.). "If you want to lay it down [Soviet leader Leonid] Brezhnev looks a helluva lot worse."

The Reagan visit was timed to coincide with the release of President Carter's budget and his State of the Union speech as well as the midwinter meeting of the Republican National Committee. It comes during a week when at least seven other potential Republican presidential candidates are in Washington.

One of them, former Texas governor John Connally, is expected to announce his candidacy formally on Wednesday. Yesterday Connally placed a series of courtesy calls to party leaders notifying them of his intentions.

During its three-day meeting, the Republican National Committee is scheduled to select the site of its 1980 nominating convention. Dallas and Detroit are considered the frontrunners. Miami, Minneapolis-St. Paul, New Orleans, New York and Kansas City, site of the Republicans' 1976 convention, have also made bids for the event.

At a meeting discussing convention rules, Sen. Barry Goldwater, the party's 1964 nominee, called for a wideopen race for the party's vice presidential nomination.

Calling the traditional vice presidential selection process "antiquated," the Arizona Republican recommended that the party select its nominee the same way it does its presidential candidate -- by open voting on the convention floor. This, he said, would "do away with this picture of both parties that the vice presidency doesn't mean much."

Sen. Bob Dole of Kansas, the party's 1976 vice presidential nominee, disagreed. Taking the choice away from the presidential nominee "would invite discord and dissension," he said.

The chief message that Reagan, the frontrunner for the nomination in early polls, brought to Capitol Hill yesterday was one of party unity. He tried to picture himself as a responsible, senior party spokesman, who had gone out of his way to campaign for Republican moderates, like Sen. Charles Percy (Ill.), as well as conservatives last fall.

He deliberately avoided controversy. Although thousands of demonstrators calling for a constitutional amendment banning abortion stood outside the Capitol, Reagan refused to address them, for instance, although he supports such an amendment.

"He came across as a knowledgeable, very pleasant guy," said Sen. Bob Packwood (R-Ore.). "He does not want to rock the boat. He values party unity above all."

Sen. John C. Danforth (R-Mo.), another moderate, emerged from his Reagan meeting saying his favorite for the presidency was still Baker, but he would support Reagan if he wins the nomination.