Sen. Howard H. Baker Jr. (R-Tenn.), who believes Congress should stay in session only half of the year and go home and mingle with the people for the rest, is offering an amendment to make the proposed Senate ethics code "self-destruct" on Jan. 1, 1980.

Not that he's against ethics, Baker hastens to add with a smile. It's just that the new code, which imposes limits on outside professional activity and outside earned income, presupposes the existence of a full-time 12-month legislature. And that's not the direction Baker thinks Congress should be headed.

Baker wants the Senate to take another look at ethics problems in three years and perhaps rethink its own current role in the constitutional structure.

He wants it to consider whether it should meet only six or seven months a year, stop dealing with tiny legislative details, be paid correspondingly less than its $57,500 current salary for each member, and have each member spend the rest of the year at home doing his or her ordinary business, like law, teaching, farming or whatever.

"That would enable members to find out what their constituency thinks and reimmerse themselves in the mainstream of the country's life," said Baker in an interview.

Baker's "sunset" amendment for the ethics code may fail, but the concept that lies behind it - a citizen-legislature instead of a full-time legislature that may become cut off from the people - has some substantial support in the Senate.

Sen. Malcolm Wallop (R-Wyo.), an articulate freshman, said that spending virtually the whole year in the capital as professional full-time legislators "tends to insulate us from the very people we profess to represent . . . We become insensitive to the effects of what we pass."

Baker, expounding his views, said, "I can ascertain a difference in attitude since 1950 when my father first went to Congress. He came up here with full expectations of returning to Tennessee regularly, keeping his family down there, keeping his interest in a range of things. He stayed in his law firm, he continued to have interests in a number of businesses."

Now, he said, Congress is moving toward a year-round status and curbs on outside earned income are the logical consequence.

Baker said he believes Congress should make back to the older concept, making itself into a policy-making and overseer body only, letting the President carry out the law, not trying to write every little administrative detail and concept into each bill.

Congress, he said, should meet from January to May for committee hearings and writing basic broad program and regulatory legislation.

Then it should go home for June, July and August, coming back for a two-month session on September and October to vote appropriations.

Members should be paid only for the time they're here, or about half to seven-twelfths of current salary. They should be allowed of current salary. They should be allowed to engage in any legitimate business, subject only to full disclosure of income and financial holdings, including disclorure of tax returns.

Acting this way, they could stay in touch with the people, concentrate on broad policy principles and still maintain oversight on the executive, Baker said.

"I'm not worried about the imperial presidency. We could have stronger oversight, oversight committees operating all year round, you could cut the legislative staff, we'd start talking about basic principles," he said.

"He'll never make it," said Richard S. Schweiker (R-Pa.). "The laws are so complex, so specific, so detailed - like a big tax bill, technology legislation - you just can't get things through in that short a time."

Sen. Gary Hart (D-Colo.) said, "What keeps us here is the number and complexity of the issues - and the desire of many people to talk about every issue. Rhetorical self-restraint would keep. I'm not sure we could successfully handle oversight. Who is going to watch the President? It's a lovely Jeffersonian concept that I share but the fact is the problems are getting more complex."

Jim Sasser (D-Tenn.) said he didn't think Baker's ideas are "very realistic. The so-called citizen-legislators became obsolete in the 1930s. The government is just too big and too complex."

Baker is nevertheless pressing ahead with his so-called "sunset" amendment. Majority Leader Robert C. Byrd (D-W. Va.) is opposing Baker because, he said the other day, "We didn't put any sunset amendment on the pay increase."