The Senate had second thoughts about financial self-sacrifice yesterday as members voted 49 to 47 to give themselves a pay raise of about $9,100 a year while also postponing a limit on their outside earnings to which they agreed only a week ago.

The vote came on an amendment to a $16.1 billion supplemental appropriations bill that was then sent to a House-Senate conference over objections from the White House, which is threatening a veto because of domestic spending allocations that exceed President Reagan's requests.

The vote on compensation would raise senators' annual salaries from $60,662.50 to $69,800, the same salary that House members voted themselves last year.

While the House voted itself a pay raise last year, the Senate did not. Instead, it dropped a limit that was to take effect on members' outside speech-making and other earnings.

This led to charges the Senate in effect was letting itself be bought; some senators last year were able to double their congressional pay through speaking fees from special-interest groups.

Embarrassed as the the amounts of income from moonlighting were disclosed, senators voted 51 to 41 last week to impose a limit of $18,200, or 30 percent of salary, on their earnings from speeches and related activities as of July 1.

Yesterday senators deferred this limit until Dec. 31. In addition, their pay raise means that the limit itself will be higher--30 percent of the $69,800 or $20,940.

The postponement brought predictions that the Senate will never allow the moonlighting cap to take effect, and in any case that senators will go on a speech-making binge for the next six months to beat the deadline.

"There's going to be an Oklahoma land rush to get speaking engagements around here," said Fred M. Wertheimer, president of Common Cause, a self-styled citizens lobbying group, who backed the pay-and-honoraria trade-off despite misgivings about the delay. Heavy speech-making schedules "may be the best guarantee against repeal; they won't be around to do it," he added.

"I will wager anything . . . that come Jan. 1 of 1984 there will be no cap. We have once again postponed the problem," Sen. Lowell P. Weicker Jr. (R-Conn.), who described Congress' handling of its own pay as a "pretzel of political posturing," said.

Weicker, arguing that "you get what you pay for," proposed earlier that the Senate pay itself $100,000 a year and ban all honoraria from speech-making on grounds that senators should be "paid out of the United States Treasury . . . not corporate treasuries." He was defeated, 89 to 6.

The Senate also defeated, 84 to 9, a proposal by Henry M. Jackson (D-Wash.) to lift members' pay to $80,100, the same amount Cabinet members receive.

The pay increase and honoraria delay was then proposed by the bipartisan leadership and was backed by Jackson, who spearheaded the fight for the honoraria cap last week.

"I think Congress is institutionally incapable of setting its own salary," Majority Leader Howard H. Baker Jr. (R-Tenn.) grumbled as he tried to help the Senate out of the mess it created for itself last week.

But the leadership proposal almost was defeated, and was saved only by last-minute vote switches under leadership pressure.

Among the reluctant supporters was Sen. Jake Garn (R-Utah), who protested that the Senate was using a double standard to impose restrictions on outside honoraria by less affluent senators while imposing no limits on investments by rich senators. "We have never seen the Senate more at its worst . . . . The whole proceeding is incredibly offensive to me and brings discredit on this body," Garn said.

"We're fast becoming a body in which only the most affluent can serve," added Sen. John G. Tower (R-Tex.).

Garn, Tower and others indicated they will push in the future for restrictions on unearned income, or at least more detailed public disclosure of assets and investments.

While the Senate could try to reverse the honoraria ceiling before January, Wertheimer said the House would probably block such action in hopes of using outside income limits for senators as leverage for pay raises for both houses. It was the House that started this year's pay controversy by proposing a 30 percent limit on outside earnings of senators.

The House is not expected to object to the senatorial pay raise but it was not clear yesterday whether it would contest the postponement of the ceiling on honoraria.

There are also other major issues for a conference to resolve in the supplemental money bill, including an $8.5 billion Senate add-on to increase U.S. support for the International Monetary Fund and a House proposal, rejected by the Senate, to ban leasing of federally owned coal through Sept. 30, the end of the 1983 fiscal year.

When the Senate began work on the supplemental appropriation last week, it exceeded administration requests by roughly $650 million. But Senate Appropriations Committee Chairman Mark O. Hatfield (R-Ore.) said he hoped to whittle off enough in conference to satisfy the White House.

However, the Senate added $400 million more, half of it to finance health insurance for the unemployed if legislation to provide the insurance is passed this summer. The appropriations bill was approved by the Senate, 64 to 33, not a sufficient number of yes votes to override a presidential veto.