The excruciating financial burden of holding elective office-keeping two homes, buying lunch, drinks, flowers and the like-has prompted Congress to consider voting its members a $50-a-day income tax deduction.

But that was only the half of it yesterday on Capitol Hill.

As a House Ways and Means subcommittee took up a bill to boot legislator' tax exemptions, the Senate was reaffirming its earlier suspension of a strict limitation on outside income.

By a 54-to-44 roll-call vote, on which 18 senators switched their opposition of two years ago, the Senate suspended at least until 1983 a yearly limit of $8,625 on outside income.

The Senate vote and the new House move to give federal and state legislators additional tax advantages seem almost certain to stir more controversy over the way Congress deals with its finances.

Fred Wertheimer, vice president of Common Cause, the lobbying group that had pushed for strict Senate income limits, said, "In a period when the American people are being asked to make many scarifices, the U.S. Senate has said, "No sacrifices for us".

But the theme being struck in the Senate yesterday-and, indirectly, in Ways and Means-was voiced by Sen. Ted Stevens (R-Alaska), who asked, "Do we have to become financial eunuchs to come to the Senate?"

One answer was offered by Rep. Dan Rostenkowski (D-I11.), who, with other House members, is pushing a bill to allow members of Congress to qualify for a $50 deduction about 270 days a year, thus reducing their taxable income approximately $14,000 annually.

Members of Congress now qualify automatically for a $3,000 deduction from their $7,500 annual salaries-a benefit designed to help offset the cost of maintaining residences here and at home, plus other expenses of office.

The Rostenkowski bill would let federal legislators deduct $50 a day for each day Congress is in session, including weekends and days of committee hearings when neither chamber is meeting.

He estimated that the deduction would apply between 260 and 270 days a year, costing the Treasury about $2.5 million annually in lost tax revenue-an average of around $4,600 for each of the 535 members of the House and Senate.

After a brief hearing of the subcommittee he chairs, Rostenkowski said the bill will be voted on next week and sent to the full Ways and Means Committee for consideration.

He said, however, that he would go along with a suggestion made by Donald C. Lubick, assistant treasury secretary, that the deduction be limited to $9,000 a year-that is, $50 for 180 days.

Rostenkowski said the whole subject is a "sensitive issue," and Lubick agreed, but he said there is no question of the legitimacy of allowing legislators of deduct part of their living expenses away from home as a business cost.

Lubick said that if the $3,000 deduction had kept up with inflation since it was adopted in 1952, it would today be about $8,000. He said the 180-day limit on a $50-a-day deduction-the $9,000 maximum-would be a fair figure to settle on.

"We are constantly criticized in the press for doing something for ourselves," Rostenkowski lamented, but he said he thought the public would be understanding about the legistators' needs.

"I'm sure the Treasury proposal will be acceptable," he said, "but there will be many questions. I like the 180-day spilt-you make it easier for a member . . . he has no records to keep [for itemization]."

Rep. Kenneth L. Holland (D-S.C.), a subcommittee member, said the legislators' major expense is maintaining two residences-one here and another in the home district.

"It's a political necessity to have a home in your district-iths a hell of an issue if you don't," he told Lubick. "To indemnity us against defeat some way sure would help us."

Rostenkowski's bill also would allow state legislators to continue receiving a $3,000 tax deduction for living expenses at their state capitals or to take a $44-a-day deduction, the same that business representatives are granted for away-from-home expenses.

Two representative of the National Conference of State Legislatures urged the subcommittee to adopt the Rostenkowski approach, but both objected to Lubick's suggested 180-day limit.

"Do no institutionalize this," said Robert Plourde, a New Hampshire state representative. "Those of us who serve are on the job at least 200 days, and we have statistics to back it up."

In the Senate, yesterday's vote followed days of parliamentary maneuvering that stemmed from its March 8 action-a voice vote that suspended the outside income limit that was to have taken effect on Jan. 1 of this year.

That limit, which would have been 15 percent of a senator's annual salary, was adopted two years ago as part of a package to win agreement on a 22.9 percent pay increase that was voted at the time.

With yesterday's vote, senators will now be bound by a previously legislated limit of $25,000 a year, which applies only to outside income from speeches. There is no income limit on other outside activites.