In the first hard slap at President Reagan's strategic weapons program, a powerful Senate subcommittee voted unanimously last night to stop the MX missile in its tracks.

Not until President Reagan decides where he wants to put this new land-based missile, the Armed Services strategic and theater nuclear forces subcommittee decided, should any more money be advanced to build MXs or prepare existing Minuteman silos to house them temporarily.

The subcommittee action, if sustained by Congress, as is thought likely, would save about $2.2 billion. Reagan had earmarked $1.5 billion to manufacture the first nine missiles and $715 million in research funds to restructure Minuteman silos.

Armed Services Committee Chairman John G. Tower (R-Tex.), who did not attend yesterday's closed session, favors the subcommittee decision, sources said.

His support virtually guarantees that the fiscal 1983 Pentagon authorization bill the committee expects to send to the floor before the Easter recess will recommend that Congress force the president to chart a new course for the controversial MX missile.

Subcommittee Chairman John W. Warner (R-Va.) said last night that the action was "a bipartisan effort to redirect and strengthen the president's strategic program." Warner said his review of Pentagon testimony about putting MX missiles in Minuteman holes just did not add up, "so we took the bit in our teeth."

The subcommittee did not try to kill the MX; instead, the bipartisan effort was to delay production so that the missile will not be ready for deployment until the permanent basing scheme has been agreed upon.

The idea is to deploy the missile in 1989, when the Air Force expects to have a permanent basing scheme, instead of putting it in Minuteman holes beginning in 1986.

Last night's vote represents the biggest single rejection by any congressional panel of Reagan's plan for closing the "window of vulnerability" he deplored during the 1980 campaign. That "window" refers to the Pentagon assertion that existing U.S. land missiles, which stand still in silos underground, are vulnerable to highly accurate Soviet nuclear warheads.

President Carter's plan was to rotate 200 MX missiles among 4,600 cement garages in Nevada and Utah so the new system would be hard for the Soviets to knock out.

Reagan ridiculed the "multiple protective shelters" scheme during his campaign. On Oct. 2 he announced that he would put the first MX missiles in Titan silos, which were to be additionally fortified. He promised to look at permanent basing possibilities, including putting the MX aboard giant aircraft and inside mountains. The Titan idea has since been abandoned in favor of putting the first MX missiles in Minuteman silos.

Tower and other critics have said Reagan's MX plan would not close the "window of vulnerability" because any missile standing still would be relatively easy to destroy. Disappointed Air Force leaders called the Reagan MX package "a decision not to decide."

It was against this backdrop that Sen. Gary Hart (D-Colo.) offered an amendment at yesterday's subcommittee session calling for an overhaul of the MX program. He also issued a news release, which said: "Silo-based MX missiles will be no more survivable, perhaps even less so, than the systems they are designed to replace."

Sen. Carl Levin (D-Mich.) released a letter he wrote to Warner calling for about the same restructuring of the MX program as Hart had recommended and the committee approved with minor changes.

Defense Secretary Caspar W. Weinberger has refused to alter Reagan's temporary basing scheme for the MX, telling congressional committees that the alternative to putting the missiles in Minuteman silos, starting in 1986, is to let them pile up in warehouses.

The bipartisan support for yesterday's subcommittee action, unhappiness in the House over Reagan's strategic program and the widespread desire in Congress to find places to cut the Pentagon budget combine to make a major redirection of the MX program a virtual certainty.