WASHINGTON (AP) _ The Senate voted overwhelmingly today to delete $250 million from the 1992 Pentagon budget for tests on a rail-mobile MX nuclear missile. The vote came one day after the B-2 stealth bomber program narrowly survived an attempt to kill it.

In a separate attempt today to cancel a major weapons program, Sen. John McCain, R-Ariz., failed by a 90-10 vote to win approval for killing the SSN-21 Seawolf attack submarine program. Each submarine is to cost about $2 billion.

Today's 67-33 vote on the MX had no effect on the missile itself. It simply proposes ending financing for testing whether the missile can be effectively fired from a rail car. The House earlier this year voted to spend the $250 million on the test.

The existing 50 MX Peacekeeper long-range missiles are deployed in underground silos in Wyoming, and there are no plans to convert it to a rail- mobile system. The proposed test was aimed at verifying that the rail system could work.

Even though the B-2 bomber program survived Wednesday's attempt to kill it, the Bush administration's plan to eventually build 75 of the radar-evading planes appears increasingly in jeopardy.

In a 51-48 vote Wednesday night, the Senate defeated a move led by Sen. Jim Sasser, D-Tenn., to stop production of the B-2 at the 15 already authorized by Congress.

At $864 million apiece, the bat-winged B-2 is the most expensive plane ever built.

Sasser's amendment to the 1992 defense appropriations bill would have scuttled the administration's plan to buy four B-2 planes for $3.2 billion in the budget year starting Oct. 1.

In a separate vote the Senate defeated, 50-49, an attempt to cut $1.1 billion from the $4.6 billion in the spending bill for the antimissile Strategic Defense Initiative.

The closeness of the votes reflect a growing sentiment in Congress that U.S. defense priorities need reordering in light of the collapse of Soviet communism.

Vice President Dan Quayle presided over the vote on the B-2 as Senate president, in case administration supporters needed him to break a tie. Just eight weeks ago, the Senate voted by a wider margin, 57-42, to defeat an attempt to kill the B-2 program.

The bomber's future has come increasingly into question since the disclosure earlier this month by the Air Force that a July 26 flight test indicated the plane was more easily detected by radar than originally expected. The Air Force says the problem can be overcome, but critics have expressed doubt.

Even considering the defeat of the Sasser effort to halt production, the administration is far from gaining final congressional approval to buy the four B-2s it wants in 1992. The Senate appropriations bill stipulates that the $3.2 billion for the planes cannot be spent until a separate vote is taken next year. It also says the plane must pass certain flight performance tests.

The House appropriations bill contains no money for new B-2s and ends production at 15 planes. House-Senate negotiators will work out a compromise bill this fall.

President Bush has said he will veto a defense bill that lacks money for the B-2.

Sen. James Exon, D-Neb., opposed Sasser's amendment but said so many former B-2 supporters were switching their allegiances that he believed the Senate eventually might end production before 75 planes are built.

Sen. Carl Levin, D-Mich., said he could not see a reason to build more than 30 B-2s, although he voted with the B-2 supporters in Wednesday night's vote.

Sasser's amendments came on the opening day of debate on the $269.7 billion defense spending bill. Among other provisions, the bill would reduce active- duty military forces by 106,000 people in 1992 and reduce the ranks of the National Guard and reserves by 35,000. Besides taking aim at the B-2 and SDI, Sasser proposed canceling $250 million earmarked for research on making the MX intercontinental ballistic missile transportable by rail. No vote was taken on this amendment Wednesday.

''All three are anachronisms,'' Sasser said. ''They are Cold War relics that we keep trying to readapt to a world that will no longer have them.''

Sasser said the foundation for his argument against the B-2 was a concern that military spending in general was too high at a time of growing budget deficits.

Sen. Ted Stevens, R-Alaska, said Congress has approved spending of more than $30 billion on the radar-evading plane since the program began more than a decade ago.

''This amendment would completely abandon that investment,'' he said, and leave the United States without an advanced long-range bombing capability in the early 21st century.