One day recently President Carter received and read a devastating intelligence report that appears to eliminate all lingering doubt that the 1979 Sverdlovsk explosion resulted from germ warface, a finding that now confronts Secretary of State Edmund Muskie with a hard test of his U.S.-Soviet policy.

In chilling detail, the report states, on the strength of a wide number of intelligence sources, that the "first casulalties were a fairly large number of male [military] reservists at the military installation," site of the biological warfare laboratory that mysteriously exploded in April 1979. The report says the commander of the military installation committed suicide and that Defense Minister Dmiriy Ustinov made an unannouced inspection two weeks after the explosion.

The Carter administration admitted on March 18 that it suspected Soviet germ warfare experimentation after preliminary reports of the deadly accident filtered through Soviet secrecy to the West.

Now, Muskie confronts two choices: charge the Russians with violating the 1975 treaty banning germ warfare experimentation or production, or sweep it under the rug at a time of heightened U.S.-Soviet tensions.

Complicating the answer are grave new questions linking Soviet violation of the unenforceable germ warfare treaty to American efforts to verify Soviet compliance with treaties on strategic arms limitation and nuclear testing. U.S. skeptics have always warned that without verification, Moscow will cheat the U.S. blind. Also at stake, as the untutored Muskie comes to grips with American policy toward the Soviet Union, are specific -- but unpublicized -- demands of U.S. friends for immediate international policing to force compliance with the germ warfare treaty.

This effort is being led by Sweden, which with other European states has reacted with understandable horror to the mysterious Sverdlovsk disaster. Muskie's prodecessor, Cyrus Vance, and the ardent U.S. Soviet detentists who advised him flatly rejected Sweden's pressure at the recent Geneva conference called to review the unenforceable 1975 treaty. Vance wanted to limit talk about the Sverdlovsk explosion and its alleged treaty violation strictly to Washington and Moscow.

"It is far too important for that," one leading European ambassador told us. "It belongs to all of us, not just to the U.S., because we are all imperiled."

Just how imperiled becomes clear from reading the lurid yet understated intelligence report recently sent to the Oval Office. The report fully justifies the demand for an immediate international move to insist on ways to enforce the germ warfare treaty.

In the past few years, the report states, the Soviets "have acquired significant technology and equipment, built large-scale biological fermentation facilities and made progress in other areas considered useful should Moscow decide to pursue production of biological weapons."

Starting in late May 1979, persistent rumors were heard on the streets of Moscow -- one of th few places where conversation is safe from police discovery -- that a "disaster" had occurred in Sverdlovsk. Workers in an adjoining Sverdlovsk institute trying to flee the fatal germ poisoning released in the explosion "were held inside the facility by security personnel." Other workers, downwind in a ceramics factory, died even though they remained inside their building; ventilators had sucked in the fatal bacilli.

When Soviet authorities finally decided a public statement was mandatory, they blamed the deaths on infection from a slaughtered cow that had been suffering from anthrax.

But that "explanation" of the disaster as an outbreak of a "rare disease" called gastric anthrax was undercut when a Soviet general, who commanded the installation that housed the germ factory, committed suicide. Further weakening the "rare disease" myth was the unpublicized arrival of Defense Minister Ustinov, one of the three or four most powerful men in the Kremlin and a possible successor to ailing President Leonid Brezhnev.

The question of why a leading member of the Politburo would bother himself about the outbreak of a rare disease in a distant provincial city is so bizarre that the intelligence report does not address it.

Adding to evidence that the deat died from pulmonary anthrax -- breathing in of the biological agents released by the accidental explosion, not infection from touching or eating diseased meat -- is the fact that "large areas around the military installation were graded and covered with asphalt" for decontamination.

An effective lethal dose of anthrax for an average man is about 10,000 spores. Accordingly, the death of several hundred human beings indicated "an extremely large number of anthrax spores -- effectively negating any assessment of peaceful or defensive research being conducted" at the military facility.

That is the intelligence finding given Jimmy Carter, with all its dispassion. What to do about it now becomes a showcase example for Edmund Sixtus Muskie as he approaches the most important challenge in his new job -- the challenge of how to deal with the Soviet Union.