The Senate Armed Services Committee, in a party-line vote, yesterday approved continued production of MX missiles next year but limited the number for deployment in current silos to 50, half the total sought by President Reagan.

Sen. John W. Warner (R-Va.), chairman of the strategic and theater nuclear forces subcommittee and author of the committee proposal, said "50 is the maximum that should be deployed in vulnerable silos."

He added that he will seek a legislative cap on silo deployment if he can obtain "bipartisan commitment to the 100 missiles" sought by the administration.

The second 50 missiles, he said, "will be in a basing mode other than present silos."

In a closed meeting yesterday, the committee approved, 10 to 9, production of 21 new MXs in fiscal 1986. Reagan has requested 48.

The 21 would bring the total approved to 63, including 21 voted last month by both chambers for fiscal 1985.

The committee also voted, however, to fund modifications of only 18 silos to permit deployment of MX missiles in existing Minuteman missile silos.

Added to 33 modification sets funded in previous budgets, that would allow 50 missiles to be based in Minuteman silos in Wyoming and one for a test facility.

The production cut and deployment limit are the most recent of several expressions of congressional concern about further MX production.

All committee Democrats opposed Warner's proposal. Some, such as Edward M. Kennedy (D-Mass.) and Carl Levin (D-Mich.), sought to end MX production next year. Others, including Sam Nunn (D-Ga.) and John C. Stennis (D-Miss.), favored building 12 MXs and capping deployment at 40.

During yesterday's committee markup, according to a source who was present, members said they expect the Democratic-controlled House to vote to reduce MX production to zero next year.

Reagan has said failure to approve the MX program would undercut U.S. negotiators at the Geneva arms talks, but critics have said the missile has no clear military purpose and is mainly an inviting target.

A Pentagon official involved in the MX program noted yesterday that the Armed Services Committee proposal is similar to a 1982 Air Force plan, rejected by the committee, to base 40 MXs in Minuteman silos while searching for a more permanent basing mode.

This official said that, "given the current constraints and deficits," the committee action is understandable. He added that the 21-missile program would cost about $2.2 billion, almost $1 billion less than the number of missiles the president seeks.

He added, however, that a 12-missile production level is "below minimums for economic production."

The committee action came as it began working its way through the defense-authorization bill for fiscal 1986.

In other actions, the panel:

* Approved a subcommittee proposal for alternative levels of reductions between $750 million and $150 million in Reagan's $3.7 billion request for the Strategic Defense Initiative, or "Star Wars," missile-defense program. The levels would be based on how much the committee decides to cut from the administration's $307 billion fiscal 1986 request.

Committee Chairman Barry Goldwater (R-Ariz.) had subcommittees mark programs for a funding level that called for zero growth plus inflation over this year's budget, along with 3 percent and 4 percent growth levels.

Sources said he indicated that he plans to report out a bill at the 3 percent mark.

* Restored funds for the Air Force to develop the C17 cargo plane cut by a subcommittee.

* Reduced procurement funds for the next Trident submarine.

* Eliminated one oiler and one mine-countermeasure ship but left most shipbuilding requests untouched.