Congress, rushing to meet a midnight deadline extended in the Senate when its official clock was stopped at 11:50 p.m., voted early today to give itself a potentially big tax break but deny senior government executives a pay raise.

The measure, approving a huge stopgap funding bill for the government, was hammered out earlier yesterday by House and Senate conferees. It also provides virtually automatic increases in congressional salaries for the future.

But Senate conferees torpedoed an unexpected last-minute proposal from their House counterparts for about a $3,000 increase in the current annual congressional salary of $60,662.50 for the fiscal year starting today.

In addition, senators would receive one additional goody: repeal of the Senate's $25,000 limit on annual income earned from speechmaking and other outside activities. House

President Reagan's news conference will be telecast live at 2 p.m. members would continue to be subject to a $9,100 limit on extracurricular earnings.

The changes were part of the emergency funding measure that had to be passed by midnight to keep the government operating while Congress tries to churn out its regular appropriations bills for fiscal 1982. None of those has been enacted.

The House approved the measure by voice vote shortly before 11 p.m., and the Senate approved the overall measure, 64 to 28, with a much closer vote of 48 to 44 on the tax break and outside earnings limit. Although its clock read 11:50 p.m., the Senate finished action on the bill at 12:27 a.m.

Congressional leaders were fighting to avoid disruption of government agencies as well as an unplanned pay increase for federal judges, whose salary would increase automatically with a lapse in the existing federal pay cap and could not then be lowered because of a constitutional prohibition on lowering the pay of federal judges.

Congressional sources said the pay of the chief justice would increase from $92,400 to $96,800, Supreme Court associate justices from $88,700 to $93,000 and District Court judges from $67,000 to $70,300.

The clock on the wall of the Senate chamber stopped at 11:50 p.m., apparently meaning the Senate would claim that the bill had passed on time, at least according to its official clock.

Sen. Dennis DeConcini (D-Ariz.) rose shortly after midnight to protest the clock stoppage. "I think we look pretty darn foolish here," he said, urging that the clock be restarted.

Sen. Majority Leader Howard H. Baker Jr. (R-Tenn.) angrily refused, claiming, "This is certainly not a new practice, and I suspect it's not the last time it will happen."

There was no indication of when Reagan will sign the bill, and Senate sources indicated that, despite the clock-stopping, the judges probably will receive their raise.

The funding bill, called a "continuing resolution," provides for spending through Nov. 20 at current levels or new levels already approved by the House, whichever are lower. This is essentially what the House had proposed. The Senate had approved language that would have allowed somewhat higher spending levels.

The conferees' jockeying over salaries and expenses amounted to another chapter in the continuing saga of how to ratchet up congressional compensation without appearing to approve a pay increase. Congress often flinches on this pay issue, and does so at the expense of high-level bureaucrats, whose pay is linked to that of members of Congress.

The House, especially sensitive to the pay issue, ignored it entirely in its version of the spending resolution. But the Senate, in approving its version last week, voted to repeal the $3,000-per-year limit on the deductions that House and Senate members can take for living expenses in Washington.

The Senate also voted to lift the limit on its members' outside income, and then, in a gesture of balanced generosity to the executive branch, also approved an increase of nearly 15 percent in the current cap on civil service salaries, which would raise the top pay for career civil servants from $50,112.50 to $57,500.

The proposed increase in the federal workers' pay ceiling would have cost an estimated $217.5 million the first year.

If the limit on congressional living-cost deductions is repealed, thus allowing members the same deductions other taxpayers may take when living away from home on business, it will cost the Treasury, and save members, more than $3 million, the Joint Committee on Taxation estimates.

The committee calculated that it would give a typical member of Congress a deduction of about $13,500 a year. There would be no cost to the Treasury in repealing the limit on earned income, although it could add considerably to the income of many members.

Figuring that the Senate proposal, especially lifting the income limit, wouldn't do as much for House members as senators, the House conferees yesterday proposed that members of Congress also be given an immediate 4.8 percent pay increase, which is what President Reagan has proposed for federal workers as a whole.

But Senate conferees rejected an omnibus House pay proposal that included the immediate salary increase for members of Congress. In the end, the conferees settled for a compromise that would give the senators their unlimited earnings from outside activities while providing for what is expected to be automatic annual increases in congressional pay after 1982, pegged to cost-of-living increases for civil servants.

In arguing over the pay increase for Congress, Sen. William Proxmire (D-Wis.) protested that the Senate had approved the tax break and repeal of earnings limitations on the assumption that there would be no general pay increase.

In a footnote to yesterday's action, Sen. Mack Mattingly (R-Ga.) briefly suggested that the conferees deny funds during the life of the continuing resolution to the Library of Congress to continue reproducing features such as "Ribald Classics" from Playboy magazine in Braille for the blind.

He dropped the idea after some conferees protested that the move would amount to censorship, and one voice was heard to say, "It's too bad they can't put pictures in Braille."