The small missile recommended by the president's advisory commission on U.S. arms would weigh about 30,000 pounds, or 15 tons, not 30 tons as reported yesterday.

The small, single-warhead nuclear missile that the president's advisory commission on arms recommended this week as a possible successor to the MX would solve some problems the Pentagon faces. But it would create some new ones.

Among other things, it might cost more than twice as much as the MX, some experts estimate. One reason is that it might require as many as 47,000 people just to tend a sizeable small-missile force of the kind now envisioned.

One important advantage of small missiles, supporters say, is that they make less attractive targets than large ones like the multiple-warhead MX. If the United States and Soviet Union shifted to smaller missiles there would be less temptation for either side to strike first in a nuclear war in hopes of knocking out the other's retaliatory power.

Supporters also argue that the small missile--30 tons vs. 100 for the MX--would be relatively easy to move around or otherwise protect. The likelier U.S. missiles are to survive an attack, the more deterrent value they have.

Whether a small missile of the kind envisioned can be built is not in doubt. It is a relatively easy job.

But how it might be transported and protected from the blasts of even distant nuclear explosions, how much it would cost, how many would be needed and how many persons it would take to operate and guard such a system are very big question marks.

In addition, it is not clear that all the important elements of the U.S. Air Force, which would be charged with developing the missile, are unified behind the idea.

Some Air Force estimates submitted to the presidential commission, according to military and industry sources, forecast costs of $69 billion over 10 years to develop, deploy and operate a force of about 1,000 such missiles on mobile transporters specially designed to withstand nuclear blast, heat and radiation.

"Don't forget," one officer said, "1,000 single-warhead missiles means 1,000 guidance systems, 1,000 transporters, 1,000 a lot of things."

The Air Force says its small-missile cost estimate compares with roughly $30 billion over the same period to deploy 100 MX missiles, with a total of 1,000 individual warheads on them, in the Dense Pack basing system that was rejected by Congress but which the Air Force said it believed offered a good chance for survival.

In addition, some estimates indicate that it could take 47,000 personnel to operate, maintain and guard these weapons, with the security requirements especially high if provisions are made to move the mobile launchers off military reservations and onto the nation's road system during exercises or periods of alert or crisis.

Industrial experts, who also asked not to be identified, say they believe the military estimates are far too high. For one thing, they say it is not likely that 1,000 missiles will be needed because they will be more survivable than MXs in fixed silos. One contractor estimated that even if a 1,000-missile force on protective vehicles were needed it could be done for $30 billion to $40 billion over 10 years.

There are also military concerns about whether the small missile would have enough power to carry a big enough warhead to knock out Soviet missile silos and command bunkers if the Soviets increase the strength of such underground installations.

Another question is whether a sufficiently accurate guidance system could be developed to steer the missile to its target after its transporter had raced from its peacetime base to a new firing point.

The key technical challenge, however, would come in developing vehicles able to carry the missile around at 40 to 55 mph and still protect itself, its crew and its missile cargo from atomic attack. There is considerable interest in new vehicles which supposedly can squat down and "seal themselves" to the earth to protect against blast and shock.

But such vehicles exist only on paper. The Air Force says a normal transporter without special protection would be able to withstand pressure of about 2 pounds per square inch, which means that an atomic blast within eight miles of the vehicle would destroy it.

If vehicles can be built to withstand blast pressures of 20 to 30 psi, then it would take blasts within a half mile to two miles to destroy them, military officers say. That is the kind of protection the commission was told was possible by industry specialists.

One company, General Dynamics, is building a nuclear-hardened transporter for new U.S. cruise missiles being deployed in Europe. But the hardness of those vehicles is said to be well below the goal for the new missile.

In its report to President Reagan this week, the commission recommended that while development goes ahead on the new missile, 100 MX missiles be deployed in silos now used for the existing force of older Minuteman missiles.

While agreeing with the commission's recommendation, former secretary of defense Harold Brown, a respected scientist and an influential counselor to the commission, issued a separate statement of caution.

"This new system," Brown said of the small missile, "still has many uncertainties, particularly in terms of cost and of the feasibility of hardening truck-mobile missiles or super-hardening of fixed shelters."

"For example," he said, "unless the United States can negotiate severe limits on a level of ICBM warheads, the number of single-warhead missiles needed for a force of reasonable capability and survivability could make the system costs, and the amount of land required, prohibitively great.

"We also do not know whether truck-mobile systems will be able to survive a megaton blast two miles away a megaton is the equivalent of one million tons of TNT . Lacking that hardness, the mobile system is easily barraged into destruction or forced into peacetime deployment on highways, which would raise political difficulties."

Those arguments are not unlike others that repeatedly have thwarted attempts by Carter and Reagan to deploy the MX in a more survivable manner.