The Soviet Union has withdrawn its "categorical" objection to the United States' stuffing widebodied civilian transports like the Boeing 747 full of cruise missiles, administration officials said yesterday.

Pentagon strategist from Defense Secretary Harold Brown down have been pushing hard for a new mother plane to insure that cruise missiles could overwhelm any future Soviet defense by giving it too much to handle.

A wide-bodied transport could carry 60 to 80 cruise missiles; esisting B52 bombers could carry about 20.

The Soviets during recent arms negotiations in Geneva backed off their flat-out opposition to wide-bodied jets performing as cruise missile carriers but pressed for several limiting conditions, officials said.

One condition sought by the Soviets but still at issue is building the wide-bodied jet from the ground up a a missile carrier rather than converting existing passenger planes to that role.

Soviet negotiators, sources said, contend they must be able to tell a missile carrier from a passenger plane at a glance - presumably by spy satellites.

A Boeing 747 McDonnell-Douglas DC10 or other passenger jet selected for the cruise missile role would have to have clearly distinguishable doors and other characteristics identifying is mission to satisfy the Soviets.

This apporach would cost the United States considerably more money than converting existing airliners. But U.S. stragegists believe the extra cost would pay off in terms of keeping the offense ahead of the defense.

U.S. negotiators at the strategic arms limitation talks (SALT) in Geneva are arguing that a wide-bodied jet full of cruise missile should count as one vehicle under the agreed-upon limit of 1,320 missiles and bombers carrying more than one nuclear warhead.

Under that rationale, the UNited States could deploy 1,200 multiple warhead land and submarine missiles plus 120 cruise missile carriers.

If all the 120 carriers eventually became wide-bodied transports carrying 70 cruise missiles each, Soviet defenders would have to contend with 8,400 warheads - an unenviable task.

One the more comforting side, backers of the cruise missile carrier argue, a cruise missile flies so much more slowly to its target than a ballistic missile that the Soviet would not have to worry about a surprise cruise-missile attack knocking out their land-based missiles.

The cruise missile force, while overwhelming in numbers, would be clearly for retaliation and thus discourage the Soviet Union from starting a nuclear war in the first place, according to Carter administration officials.

Rather than go along with the United States by counting the wide-bodied missile carrier as one bomber within the 1,320 limit, Soviet negotiations have said each jumbo jet should count as three times as many missiles as the B52. The United States is rejecting this argument.

Secretary Brown's enthusiasm for using wide-bodied jets as cruise missile carriers is not shared by the House Armed Services Committee. It recently deleted the entire $41.2 million the Pentagon is requesting in its fiscal 1979 budget for the jumbo jet missile carriers.

A wide-bodied jet serving as a missile carrier would be so slow that Soviet defenses could knock it out of the sky, the House committee argued, also, it said, the concept amounts to putting too many nuclear eggs in one basket.

The committee majority voting against the new missile carrier further predicted it would end up costing as much as the $100-million-a-copy B1 bomber which President Carter canceled. The B1 could have carried cruise missiles as well as penetrate defenses on its own.

While conceding a 747-type jet loaded with cruise missiles would be slow and easy to hit, backers stress that it would launch its cruise missiles while still safely out of range of Soviet defenses.

As Soviet defenses improved, the proponents argue further, the range of the cruise missiles could be extended beyond the 1,500-mile limit envisioned under the SALT agreement now in negotiation.

The Senate Armed Services Committee, in marking up its version of the Pentagon money bill, so far has gone along with authorizing money for the cruise missile carrier, although there is still a chance the requested $41.2 million will be shaved a bit.

The Air Force is running a competition between aviation companies to test the concept of using wide-bodied jets as cruise missile carriers. Specialists see no big technical problems.

However, diplomatic and political problems still loom large as the United States strives to hinge much of its strategic offense on the cruise missile.