The Reagan administration and a blue-ribbon panel of outside experts studying the future of the controversial MX missile are moving toward a proposal that discards major elements of the original basing plan and revives the possibility of an antiballistic missile defense system.

Senior officials stress that no final recommendations or decisions have been made.

But interviews with several persons in and out of government who are close to the deliberations suggest that a compromise is emerging that offers something for everybody.

It will allow, sources say, the administration to start modernizing the land-based component of the U.S. strategic nuclear missile forces with the MX, keep open several different options for the future and soften some of the political oppositions to the previous proposal for a massive MX deployment in Utah and Nevada.

The key elements and options reportedly include:

Putting the MX missile into production while scaling down, at least initially, the original deployment plan, which called for shuttling 200 missiles among 4,600 underground shelters in Utah and Neveda. Under consideration is a plan that would cut that deployment roughly in half, clustering fewer missiles and shelters in fewer valleys and reducing the environmental impact and cost.

Doing preparatory work that would allow MX missiles to be placed in underground silos now used for older Minuteman and Titan missiles in other states. This option would allow the first MX missile to be fielded roughly one year earlier than at the Utah and Nevada bases.

Accelerating research, development and testing, though not necessarily deployment, on an antiballistic missile (ABM) defense system to protect silos from Soviet attack.

Beginning a study of funding needs for a missile smaller and lighter than MX that, several years from now, could be produced in large numbers and moved around the country by road, plane or rail so that it would be relatively invulnerable.

Accelerating development of the advanced (D5) version of the submarine-based Trident missile, which several years hence, would give the Navy the same ability to destroy Soviet missile silos that MX is supposed to have. The possibility of putting MX to sea, an option once favored by Defense Secretary Caspar W. Weinberger, is now viewed as dead.

The idea behind these options is that they allow the basic MX to move ahead while work goes on with the other approaches.

For the Reagan White House, the questions of whether and where to deploy MX are crucial. This is partly due to the missile's $35 billion-to-$60 billion price tag and political opposition to constructing huge new bases in Utah and Nevada.

But is also will set the tone for the future composition of the U.S. Nuclear arsenal and nuclear strategy, and it will undoubtedly have a lasting impact on the course of both the U.S. Soviet nuclear arms race and arms control efforts.

The Air Force contends that years of studies of more than 30 possible ways to base MX repeatedly go back to the idea of shuttling the 200 missiles among 4,600 protective shelters scattered in the Great Basin of Utah and Nevada. That seems to be the best way to keep the missile safe from Soviet attack, since Soviet commanders would not know which shelters hid the missiles.

The Carter administration accepted this scheme. But Reagan, as candidate and president, has frequently said that while the United States needs the missile, he doesn't like the Air Force basing idea. Weinberger has said the same thing.

In March, rather than proceeding with the Carter plan, Weinberger appointed a 15-member panel of nongovernment experts to take still another look at where to base the MX and report recommendations to him by July 1. That group is formulating its recommendations and Weinberger says the conclusions will be seriously considered by the administration.

The governors of Utah and Nevada are opposed to the multiple-shelter scheme. The issue has also put on the spot key conservative senators such as Paul Laxalt of Nevada and Jake Garn and Orrin G. Hatch of Utah, who are close to Reagan and who otherwise support a big defense buildup. Since the panel was commissioned, the Utah-headquartered Mormom Church has come out against MX.

But a compromise plan, some sources say, may be easier on local politicians because it does represent a cutback and suggests the administration has done something to take their concerns into account.

At the same time, it will avoid total abandonment of the original plan, which could cause trouble with U.S. allies in Europe if they see political opposition here succeeding at getting rid of land-based missiles. European governments now face protest movements because the United States wants to put medium-range missiles there.

A recent public opinion poll by Cambridge Reports Inc. for a group of companies interested in MX reportedly shows more support for MX nationwide than expected. These figures sources say, will be presented to the White House this week.

The figures reportedly show a slight majority against MX in Utah and a plurality for it in Nevada. But the most striking statistic shows 73 percent nationwide "more inclined" to accept the Nevada Utah plan for MX if, after absorbing the panel report, the president voices his support for it.

Several sources said that what MX needs most is some overt presidential backing for a specific plan that would take advantage of Reagan's popularity. b

Administration officials says that ultimately the final MX decisions will center on whether the system can be fielded that will not have its invulnerability overcome in due course by the Soviets and which does not have to rely on future-arms control agreements for security.

The Reagan administration has made clear it does not think much of the Strategic Arms Limitation Talks (SALT) that have produced U.S.-Soviet agreements by the Nixon and Carter administration.

Top Pentagon officials also say it is important to point Moscow toward decisions that are best for both sides in ultimately removing threats to each other's forces. As one official explained, systems should be fielded that make clear, if Moscow responds in a threatening way, that the United States could move relatively easily into another more sophisticated stage, which would complicate the Soviet's problem still further.

Precisely how this could be assured, however, has never been spelled out nor, as one senior official points out, does the administration have a clear strategy of what it wants in its missile force. This, he says, is being worked out.

Furthermore, he acknowledges that despite the general public support for increased defense spending, the administration faces a major problem in that it is embarking on a new bomber, new missile and possibly new ABM program at once, in addition to big increases in other military spending. "We just can't afford to break the bank," he adds.

The options of putting MX into Minuteman silos and developing an ABM also have problems.

The nation has 550 of the most advanced Minuteman III missiles, each of which carries three atomic bombs in its nose, and 450 of the less sophisticated single-warhead Minuteman II.

By replacing some of the Minuteman II with MX, the nation would also be increasing the number of warheads because MX will carry 10 bombs in its nose. Similarly, it is argued that with MX mixed with Minuteman the number of missiles surviving any Soviet strike would contain a larger number of warheads available for retaliation.

But the main reason for going ahead with MX is the claim by both the Carter and Reagan administrations that the Minuteman force, in its fixed bases, is becoming vulnerable to Soviet attack. That is, where the missile defense option comes in as another way to introduce uncertainty into Soviet attack plans.

But specialists acknowledge a decision to build and deploy an ABM would likely touch off another huge argument in the country, as was the case in 1969, and that it would also involve either amending or possibly even ending the 1972 Soviet ABM limitation treaty.

As a result, they say, it is important to do a lot of testing first to make sure the system would work and to convince people it is needed.