President-elect Ronald Reagan's designated congressional liaison, Max Friedersdorf, expects the new president to enjoy a long and lovely honeymoon with Congress, but not an indefinite one. The marriage will take a little work.

But he expects a lot of help from the Republican members of Congress. "I sense a tremendous desire to present a united front," he said at a National Press Club breakfast yesterday. "We've been in the minority so long, I don't think they're going to blow it."

GOP control of the Senate will help keep the bloom on the rose, and the liaison office plans to cultivate the conservative support Reagan has in the House, Friedersdorf said, adding Reagan will meet regularly with the Republican leadership and will have regular bipartisan meetings as well. As for his Democratic in-laws, Friedersdorf said, Reagan plans to meet with the Democratic leadership "at least once every three weeks."

Friedersdorf also said he expects all the members of the Cabinet to be confirmed by Inaugurtion Day, in time for a swearing-in ceremony in the Capitol after Reagan takes the oath of office.

Even the toughest confirmations -- those of Secretary of State-designate Alexander M. Haig Jr. and Interior Secretary-designate James Watt -- will get through the Senate "in good shape," Friedersdorf said.

Haig got some well-placed support yesterday, including a statement from Sen. Sam Nunn (D-Ga.) on the floor of the newly convened Senate. Nunn said he recognizes "the legitimate and rational concern" about a military officer heading the State Department, but added that "few Americans . . . have the degree of foreign policy expertise and strategic grasp" of Haig. He said he plans to support Haig's confirmation.