The special presidential commission studying U.S. strategic nuclear forces is leaning toward recommending the phased deployment of up to 200 new MX missiles, twice as many as were proposed in earlier Reagan administration plans that Congress rejected.

The missiles would be placed in existing Minuteman silos.

Sources say no final decision has been made on the number of missiles to recommend to the president next month. The 11-member commission has heard suggestions ranging from 20 to 200. But the sources say a majority of the commission members and eight special counselors now seem to favor the higher figure, even though it could prove controversial on Capitol Hill.

The main reason is said to be a feeling among many members that President Reagan genuinely wants an arms control agreement with Moscow and that this higher starting point will strengthen his negotiating position and give the Soviets more incentive to reach an accord.

The commission may recommend that the new missiles be deployed in stages. For example, if the commission does decide on 200 missiles, it could recommend that these be deployed in an initial phase of 100 with further groups of 50 to follow.

Officials say the commission is seeking a deployment plan that on the one hand will be a "resolute" statement that the administration plans to modernize the land-based missile force, yet on the other hand will leave Congress year-by-year budget control over that force's size.

Members also are said to feel that a higher deployment figure would be more cost-effective in the long run, in that economies of scale will cut the cost of each missile.

If it is not decided to recommend 200 missiles, then a level of at least 100 is viewed as a minimum, with anything smaller seen as having little negotiating value but high cost.

The other basic decisions of the commission are all said to be made.

There is agreement that the United States should seek to keep up all three legs of the so-called nuclear triad: land-based missiles, submarine-based missiles and long-range bombers.

Nor do members dispute the need for the MX, although there could be one objection among the counselors.

No new missile silos would be built. As MXs were deployed, comparable numbers of Minutemen, of which there are now 1,000, would be retired.

It will probably be recommended that the Minuteman silos be strengthened to increase their chances of surviving a first strike by Soviet missiles.

But the commission is said to be skeptical that any great advance in "hardening" techniques can be achieved quickly.

It will recommend further research and development work in this area.

It also will recommend speeded-up studies to see if a new and much smaller missile can be developed eventually to replace the MX.

Some theorists see a small and probably mobile missile as potentially less vulnerable than the big and stationary MX, but sources say there is skepticism on the commission about this as well.

The commission was briefed on small missiles by several defense contractors, including Boeing, General Dynamics, Bell and Martin.

But sources say it would be seven to 10 years before such new missiles could be operational, and there are questions as well about where and how such missiles might be deployed.

In short, officials say, MX is the only alternative available, given the basic decision that the Minuteman force must be modernized.

The recommendation to put the MX in existing silos is certain to be controversial.

That was the recommendation Reagan originally made in October, 1981, when he discarded President Carter's plan to shuttle and hide 200 missiles among 4,600 shelters and called instead for 100 MXs, the first of them to be installed in improved Minuteman and Titan missile silos.

Congress rejected that basing plan in part because it did not meet Reagan's campaign pledge to close the "window of vulnerability" and protect U.S. land-based missiles from Soviet attack.

In December, Congress also rejected Reagan's next plan, known as Dense Pack, which involved bunching 100 missiles close together on the theory that attacking Soviet missiles would blow each other up.

In January, Reagan named his commission of prestigious former officials and experts in hopes of finding a solution that would be technically and politically acceptable.

The commission has found no new technical solution, and its recommendation will not solve the vulnerability problem.

The commission has held 27 sessions thus far and will meet today in a key session with the Joint Chiefs of Staff, concerned about money as well as missiles.

Scores of other meetings have been held thus far with congressional leaders in search of a political compromise.

But the commission's congressional expert is still said to be pessimistic about marshaling enough support in Congress to pass the MX.

Reagan is not bound by the commission's recommendations, although the White House has been briefed continuously on the panel's progress and thoughts.