Congress yesterday put the government on emergency fiscal life-support for a third time this week as House-Senate conferees failed to reach agreement on a nearly $500 billion spending bill for the next 12 months.

It approved an extension of current funding levels through midnight Tuesday, the day Congress returns from a three-day recess for Yom Kippur and Columbus Day, although House and Senate leaders conceded that there is no assurance of agreement by the conferees on Tuesday.

The measure, which followed similar short-term extensions enacted Monday and Thursday, was approved by voice vote in both chambers and sent to President Reagan, who is expected to sign it.

All government offices are expected to reopen at their regular hours Tuesday morning. But, with the interim authority lasting only through Tuesday night, Congress will have to finish its work on the long-term bill or pass another extension to avoid a disruption in government operations on Wednesday.

Most "nonessential" government functions were canceled and workers sent home when the money ran out Thursday, but conferees agreed late that day to pay them for a full day's work.

Yesterday's conference stalled over defense and foreign policy issues and a dispute with the Reagan administration over water projects funding.

"Regardless of motives, we cannot win under any circumstances," Senate Appropriations Committee Chairman Mark O. Hatfield (R-Ore.) said as the conference broke up. "Congress," he added, "will be blamed for bringing the government to a standstill."

Senate Majority Leader Howard H. Baker Jr. (R-Tenn.), whose once widely praised leadership has been sorely tested as he prepares to retire from the Senate, said, "I feel like the fellow who's about to graduate from college and he flunks senior English."

As Congress missed its original target for adjournment by this weekend and struggled to finish its work in time for a few weeks of campaigning, there were these other developments:

*The Senate defeated a proposed "mutual, verifiable" freeze on nuclear weapons with the Soviet Union, which freeze advocates offered as an amendment to a debt-ceiling extension that must be passed before Congress adjourns. The vote was 55 to 42, somewhat closer than the Senate's 58-to-40 vote against the freeze in October 1982. The House has approved a nuclear freeze.

*A one-year ban on oil and natural gas leasing off the coasts of California and Cape Cod, Mass., was approved by the spending bill conferees in what would be the fourth consecutive annual moratorium on off-shore leases. The existing ban on leases off the Florida coast would not be continued.

*The Senate put off until next week action on the debt-ceiling measure, which would raise the government's borrowing limit from $1.58 trillion to $1.83 trillion, presumably enough to last for 12 months. The House has passed the bill as part of its final action on the congressional budget for the year.

*The House approved, 308 to 86, a bill to authorize maximum annual appropriations of between $200 million and $250 million for the nation's public radio and television system. The bill, which the Senate has passed, goes to the president, who has vetoed it once.

Enactment of the stopgap funding measure was necessary because previous interim authority expired at 6 p.m. yesterday, leaving the government without funds to reopen most agencies on Tuesday.

Congress made the latest extension last only through Tuesday because its leaders wanted to keep up pressure for prompt action on the 12-month measure, which would provide year-long funding for the departments of Defense, Agriculture, Interior, Labor, Health and Human Services, Education, Transportation and Treasury as well as several large agencies.

These departments and agencies remain unfunded because Congress has failed to pass nine of its 13 regular appropriations bills for the fiscal year that started Monday. The 12-month measure, in effect, incorporates regular appropriations bills for these agencies for the rest of fiscal 1985.

Before quitting for the weekend, the conferees resolved a number of relatively noncontroversial issues. But the larger issues, especially that of continued U.S. military aid to antigovernment guerrillas in Nicaragua, remained unresolved.

The House has proposed to block further assistance, while the Senate would continue to permit it. Senate Democrats suggested a compromise in which aid to the so-called "contras" would be allowed only through March 1, but it was rejected by Rep. Edward P. Boland (D-Mass.), author of the House ban.

The House has voted four times against continued funding for covert operations on behalf of the guerrillas, and it won't change its position, Boland said.

Disputes also were unresolved over restrictions on antisatellite weapons and spending levels for Reagan's new "Star Wars" defense initiative for space, although the overall level of defense spending for fiscal 1985 has been nailed down at $292.9 billion, an increase of 5 percent after accounting for inflation.

Most domestic spending levels have been resolved with tacit agreement from the administration, but water projects remain a major obstacle and perhaps the greatest potential threat to a final accord between Congress and Reagan.

Although its signals have been mixed, the White House has objected to proposed spending for this fiscal year and to a long-term authorization bill for about $18 billion in new projects that the House proposed to include in the bill.

Conferees were whittling away at the spending totals, getting them below $100 million by the end of the day, although the figure reportedly remained considerably higher than the White House was willing to accept.

On the bigger authorization bill -- separate from the spending bill -- conferees were deadlocked and prepared to take their differing positions back to each chamber for a further vote.

But Hatfield warned bluntly that House insistence on inclusion of the authorization would guarantee a veto and he indicated that the Senate wouldn't even consider it.

The White House has been pressing to keep down funding for water projects and White House spokesman Larry Speakes said yesterday that "we do not want a continuing resolution with this pork barrel" of water projects.

Although there was general agreement on the new interim spending bill, it ran into trouble when conservative Rep. William E. Dannemeyer (R-Calif.) tried to block action on it to force consideration of the Reagan-backed proposed constitutional amendment to encourage balanced budgets.

Dannemeyer succeeded only briefly, however. The Democratic leadership hastily called a House Rules Committee meeting to get around his objections, and the bill passed without further trouble.

In Senate debate over the nuclear freeze, Sen. Edward M. Kennedy (D-Mass.) argued that it would force arms negotiations with the Soviet Union, which, he noted, has not happened in the 3 1/2 years of the Reagan administration.

"We must reject the foolish theory that we can have fewer bombs tomorrow if we have more bombs today," Kennedy said.

But Senate Armed Services Committee Chairman John G. Tower (R-Tex.) contended that a nuclear freeze would "lock us into an inferior negotiating position" and added: "The only sure way we are going to avoid a nuclear holocaust is to deny to every nation the power to strike first." CAPTION: Picture, Hill conferees work to resolve differences between House and Senate versions of $500 billion fiscal 1985 spending bill. By James K.W. Atherton -- The Washington Post