The United States must fine-tune its nuclear forces so they could single out for destruction everything from Soviet political centers to missile silos, Defense Secretary Harold Brown told Congress yesterday.

"Our goal," said Brown in his 300 page posture statement just released, "is to make a Soviet victory as improbable, seen through Soviet eyes, as we can make it over the broadest plausible range of scenarios."

That means, he said, programming strategic missiles and bombers to hit "in the selective and measured way a range of military, industrial and political control targets" while still keeping some H-bombs in reserve.

This capability would "make it clear to the Kremlin," Brown contended that, if Russia fired nuclear weapons at the stark choice of either making no effective military response or totally destroying the Soviet Union."

In maintaining this policy has the best chance of deterring the Soviet Union from attacking the United States in the first place, Brown said he personally doubted there could be such a thing as a small nuclear war between the two superpowers.

Said the defense secretary who helped develop H-bombs in the laboratory before coming to the Pentagon:

"I am not at all persuaded that what started as a demonstration, or even a tightly controlled use of the strategic forces for larger purposes, could be kept from escalating to a full scale thermonuclear exchange."

However, the Russians might not agree, Brown warned. Therefore, the United States must be able to do anything to the Soviet with nuclear weapons that they could do to us, he said.

Brown in the nuclear policy section of his posture statement, also tried to reassure European allies, and warn the Kremlin, about U.S. determination to retaliate if Russia attacked an allied nation. Some Europeans have asked over the year's if the United States would risk its own incineration; the Hamburg for Harrisburg argument.

"Nor should any possible foe," Brown said, "believe that our hands would be tied in the event that he threatened or attacked our allies with nuclear weapons.

"He, too," Brown warned, "would place critical targets at risk, both in his own homeland and in the territory of his allies," thus undermining "his political and military ability to gain control over such vital regions as Western Europe and Japan."

Both the United States and Soviet Union are steadily improving accuracy of their ocean-spanning land missiles and submarine missiles so they could crack the other's silos before the missiles inside could be lauched.

Critics contend such "counterforce" capability will tempt both sides to fire tack, possibly a false alarm, to keep them from being destroyed on the ground. This, they warn, will destablize the balance of terror.

Another response to increasing accuracy is to make missiles mobile so they would be hard to hit, even by precision warheads. This is one reason President Carter decided to build the mobile MX mobile.

As both, sides resort to mobile missiles, there will be more pressure on the United States and Soviet Union to build more warheads to saturate the hiding places.

Brown's report verifies that President Carter has concluded the advantage of a versatile nuclear offense, including counterforce capability, outweighs the risks.