While controversy and intense lobbying surrounded the pending presidential decision on the MX missile system, Defense Secretary Caspar W. Weinberger was reported yesterday to be backing away from making any immediate recommendation on how to base the new $50 billion intercontinental missile.

Instead, according to sources both in and out of the government, Weinberger may simply ask for additional research and development money to explore several ideas for deploying the new weapons system. He is scheduled to present his long-awaited strategic defense proposals on Monday to President Reagan at a specially convened National Security Council meeting in Los Angeles.

Until this week, Weinberger and the president, according to White House sources, favored putting the MX missiles aboard a new type of transport airplane that could stay in the air for days at a time. But the so-called Big Bird plane exists only on paper at this point.

According to one source, "the secretary is going to say we can't rely on paper studies to make a decision as important as this -- we need to develop hardware to see what will really work."

Sources added, however, that the defense secretary will propose the immediate production of an advanced version of the B1 bomber along with accelerated development and construction as soon as possible of the so-called Stealth bomber, which is supposed to be able to elude enemy radar.

According to some sources, the Weinberger plan calls for construction of 50 B1s and 200 Stealth aircraft. But other sources said the secretary favors purchase of the B1 in smaller numbers to permit a rapid switch to the more advanced Stealth design when the technology becomes feasible.

The plan for an air-mobile MX has produced a storm of opposition from inside the Air Force, from powerful chairmen of defense committees on Capitol Hill and even from defense experts within the administration. Most of these groups are committed to the land-based plan, which would hide 200 MX missiles in 4,600 shelters to be spread across the Great Basin of Utah and Nevada.

While Weinberger was attracted to the airborne approach, a special panel of the Defense Science Board that he appointed recommended to him yesterday that he support the multiple land-based shelter plan for the MX along with an anti-missile defense system to protect the weapons. The land-based system has provoked considerable opposition in Utah and Nevada because of its impact on the environment and land.

The panel said that by using existing mobile radars and short-range missiles, an anti-ballistic missile system for the MX could be available "within a few years," according to one administration source.

Both the president and Weinberger have been critical of the land-based shelter plan. Reagan declared his concerns during the campaign about any MX deployment that would harm the environment in the West. And ever since Weinberger took office in January, he has been pressing Pentagon officials for a different type of basing plan.

The panel of outside experts, headed by Dr. Charles Townes, was asked to look into alternative ideas, and some of its recommendations will be among the options Weinberger is expected to seek additional money for.

These include the so-called air-mobile concept, which sources said yesterday will get significant research funding. Another approach due for additional funding is the idea of ABM defense, along the lines proposed by the Defense Science Board. A proposal to bury MX missiles in deep underground shelters, presumably invulnerable to attack, will also be pursued.

Additional research money will also be given to the next generation of submarine-launched missiles, the Trident II. This new missile would be designed to be as accurate as the MX and have warheads with explosive power equal to the land-based ICBM and theoretically able to knock out Soviet missiles in their protected silos.

There were also unconfirmed reports circulating yesterday in Washington that the Reagan administration may be preparing to abandon the MX altogether, in favor of a so-called common missile.

The common missile would be smaller than the MX but could be used for a mobile or silo-basing system on land, while at the same time adaptable to Trident submarines. The MX missile is too large, as presently being designed, to fit into a submarine or for easy mobility on land.

Several sources, however, said that Reagan and Weinberger, both of whom have publicly stated they want the MX missile, would be unlikely to drop it at this point for a smaller version that could deliver fewer warheads to the Soviet Union.

Postponing any decision on how to base the MX could result in the saving of almost $1 billion next year, sources said. But they emphasized that the idea of delay was "not driven by the budget," as one official put it. "The strategic systems are protected within the budget with even bigger bucks," he said. However, any delay on the deployment plan would likely push back the date when the giant new missile is in place, ready for operation.

The multiple-shelter land-based plan first adopted by the Carter administration set an initial deployment date for the first missiles of 1986.

"The Reagan people won't be able to make that," one source said yesterday, if the administration fails to select a basing system this year.

One alternative being pushed by some in the administration calls for a less ambitious land-based system, deploying 100 MX missiles within the vast reaches of Nellis Air Force Base in Nevada. This would lessen environmental objections about the impact on public lands.