President Reagan is prepared to recommend replacement of the disputed land-based MX missile system with an even more controversial proposal for putting the missiles aboard airplanes for aerial launching, according to administration and industry sources.

White House counselor Edwin Meesed III said the president had made no decision. But Meese gave a strong clue to the administration's fundamental opposition to any land-based MX system with this comment: "As the president said in the campaign and has said since, he is concerned about a basing mode that would severely damage the environment of several western states."

The proposal is likely to provoke significant opposition from the Air Force, which considers the proposal technologically deficient as well as from defense-oriented members of Congress who will point out that an airborne missile system has been considered and rejected by three prior administrations.

And it could provoke severe political opposition in European countries that are being asked by the United States to accept land-based missiles.

Secretary of Defense Caspar W. Weinberger denied again yesterday that any final decision had been made.

But well-informed sources both in his department and elsewhere in the administration said Weinberger was about to recommend a complete strategic package to the president that will include development of a new bomber that is a variation of the B1 canceled by President Carter.

White House sources said they expect that the manned bomber could be announced as early as mid-August while the president is vacationing in California. Both Meese and Weinberger said no decision has been reached on whether to announce the various elements of the strategic package separately or whether to do it at one time.

Regardless of how it is announced, administration sources who described the package yesterday said it will contain these elements:

Replacement of the land-based MX system advocated by the Carter administration and opposed by the Mormon Church and influential western senators, including Reagan intimate Paul Laxalt (R-Nev.), with an airborne system that would initially include putting the MX intercontinental balistic missiles aboard converted C5 transports for launching. The 100 planes with their 100 missiles would kept on alert at a string of bases throughout the country for takeoff at the first sign of Soviet attack.

While this interim airborne system was being deployed, perhaps as early as 1986, research and development would continue on three long-range systems which Pentagon planners hope could eventually replace the converted transports. One is a new airplane, known as "Big Bird," which would be designed for the 250,000-pound MX missile and its capsule, though some question whether this is technologically possible.

Another option is a revived anti-ballistic missile system to protect Minuteman silos into which MX missiles would be placed. The Soviet-U.S. arms limitation treaty of 1972 prohibits all but a limited number of ABM missiles. The third option, known as "Hard Tunnel" or "Citadel," would place missiles in tunnels at depths of 3,000 feet or greater.

Deployment of an interim bomber, similar to the B1, which President Carter decided not to build, while work continues on the more advanced "Stealth" aircraft. This proposal is favored by Sen. John G. Tower (R-Tex.), chairman of the Senate Armed Services Committee.

Deployment of an improved version of the Trident seaborne missile, known as "D5." These missiles are believed to be 60 percent more accurate, meaning that fewer would be necessary.

The plan to put MX missiles into C5 transports, known as Air Mobile, both solves and creates political problems for the administration.

Scrapping of the land-based system will make points for the administration in the president's base of western states and may make it easier to hold down defense outlays in the next two fiscal years even though the plan could ultimately be more expensive even than the $35 billion land-based program.

But Air Mobile also invites far greater damage from a hypothetical Soviet attack, because the planes would be deployed over population centers. One Department of Defense study estimates U.S. population loss in a Soviet attack against the land-based MX at 5.9 million people and at 11.3 million in an attack against Air Mobile MX.

The estimated differences become staggering in the hypotheses of a second nuclear exchange -- 6.1 million people with the land-based MX and 67 to 93 million people with the Air Mobile system.

Throughout the defense community, there is also a widespread skepticism ABOUT THE RELIABILITY OF THE air Mobile system and concern about the communications difficulties that could be created.

The Air Force, which so far has been uninfluential in the discussions within the administration, reportedly has a counterplan to try to head off the Air Mobile system. This calls for basing the MX on Department of Defense-owned land, probably at Nellis Air Force Base in Clark County, Nev.

Advocates of the Air Force alternative argue that it would enable the administration to sidestep the environmental objections to the land-based system of 200 missiles scattered among 4,600 shelters in Utah and Nevada by concentrating the system in a single desert county.

An advisory committee headed by Nobel Prize physicist Charles Townes reportedly has recommended a reduced land-based system of 100 missiles.

Weinberger, who met this week with Reagan, Meese, White House chief of staff James A. Baker, deputy chief of staff Michael K. Deaver and Secretary of State Alexander M. Haig Jr. to discuss the strategic proposals, said he also had conferred with the Townes committee but does not expect a formal report until next week.

Weinberger emphasized that the committee was only advisory but also said "it's silly to appoint a group for six months and then not listen to its recommendations."

Behind the scenes, the coming strategic decision had provoked one of the fiercest battles of the administration. It is a conflict in which some advocates of MX are worried that Weinhberger's recommendations will divide the defense community on Capitol Hill and result in no missile system at all.

Defense contractors, who have strong and differing interests in the various alternatives, are also lobbying energetically in the conflict.

From the start, the land-based MX has been tainted in administration considerations as a Carter plan. Actually, it was born in the Ford administration, which toyed with the Air Mobile concept and then discarded it.

Some sources said yesterday that former President Ford and his secretary of defense Donald Runsfeld were being asked to lobby the Reagan administration in opposition to Air Mobile and in favor of the land-based system.

One White House official said he anticipates that the president will announce support of a new bomber in mid-August and follow it up soon with his MX announcement. The official said that announcing both proposals at the same time was "under consideration."