The future of U.S.-Soviet arms control agreements is being further clouded by deepening suspicions that the Soviets have violated an existing treaty banning the production of germs for warfare.

The suspicions were aroused and subsequently confirmed to varying degrees by the outbreak of deadly anthrax in Sverdlovsk, Russia, in April.

The U.S. intelligence community has concluded after sifting through the evidence that between 40 and 1,000 Russians were killed at Sverdlovsk by breathing in anthrax, rejecting the Soviet claim that the people who died ate meat poisoned with anthrax.

Several germ warfare experts within the Defense Intelligence Agency have concluded that so much anthrax was being produced at Sverdloysk that it could only be intended for "offensive' use, not for laboratory research on how to defend the country against the deadly germs.

Neither the DIA nor any other U.S. intelligence agency is willing to make a corporate judgment to that effect yet, sources said. But Pentagon officials conceded that the unanswered questions about Sverdlovsk threaten future arms control agreements and impel military reappraisal of U.S. defenses against germ warfare.

Politicians who have supported U.S.-Soviet arms control agreements in the past are warning that new ones will be hard to sell to Congress unless the Carter administration finds a way to force the Soviet Union to tell the whole story of Sverdlovsk.

Sen. William Proxmire (D-Wis.), in the forefront of this group, is demanding that the administration make an international issue out of Sverdlovsk by bringing it before the United Nations.

But President Carter is reluctant to do that, as evidenced by a letter Deputy Secretary of State Warren M. Christopher sent last week to Proxmire.

After telling Proxmire that the administration had "raised the issue twice" with the Soviets about Sverdlovsk and "made clear to them that we are dissatisfied with their responses to date," Christopher wrote:

"Because of the gravity with which we view this issue, we are making special efforts to insure that it is dealt with in the most serious fashion, and not treated as a political ploy with which to embarrass the Soviets. This is crucial if we are to persuade both the Soviets and the international community that our concern is genuine."

In discussing Christopher's letter, Proxmire said he was "disappointed" that the State Department was not being more aggressive with the Soviets on the issue.

"We should be insisting on unequivocal answers from the Soviets to all our questions," he said. "They owe us that under the biological warfare convention of 1975.

"Nothing is quite as horrible as germ warfare," the senator continued, "and the world should be told of Soviet perfidy. If the Soviets have cheated on an important international treaty, we need to know it now rather than later when it might be too late."

The treaty is the 1975 Biological Weapons Convention, signed by the United States, the Soviet Union and 111 nations. It bans the production or storage of biological agents beyond what is needed "for prophylactic, protective or other peaceful purposes. . . ."

Since April, U.S. intelligence agencies have been trying to figure out how many spores of anthrax it would have taken to kill the Russians who died at Sverdlovsk.

"Clearly if the fatalities were at the upper end of the estimate," said one defense official in discussing the significance of the estimated 40 to 1,000 deaths, "there would have been more anthrax produced than needed for any laboratory purposes."

If it is proved that the Soviets are indeed stockpiling anthrax in preparation for wartime use, should the Pentagon follow suit and develop this germ warfare capability it abandoned?

The view at the policy level is "no" because anthrax and germs like it are too difficult to manage on the battlefield. The better response to Soviet stockpiling would be to develop defenses, including clothing and injections.

Since the 1975 treaty does not specify how much anthrax constitutes a violation, it would be difficult, given Soviet secrecy and scant U.S. intelligence on the accident, to prove Moscow went beyond developing agents for peaceful purposes at Sverdlovsk, administration officials said.

But if the congressional preception continues to grow that the Soviets are cheating on germ warfare treaties, these officials conceded, it will be harder than ever to assure already skeptical lawmakers that the Soviets would live up to SALT II or any other treaty.

The Federation of American Scientists, in its newsletter this month, called upon Soviet scientists to "provide the world with more information" on Sverdlovsk.

"The matter is taking on ever-greater importance for the future of arms control," the federation warned.

"The circumstantial evidence for such a violation arises from the fact that the epidemic in question took place in a part of the surroundings of Sverdlovsk in which there is a long suspected laboratory for biological warfare.

"Moreover, anthrax is an obvious candidate for biological warfare activities. It was one of the half dozen biological agents thought most promising in the now-terminated U.S. biological warfare program.

"Not contagious, "and thus running no risks of spreading to one's own troops," the scientists' group wrote, "its spore form is highly stable against sunlight, changes in temperature or shocks and hence lends itself to a long shelf life.

"It cannot be filtered out by the nose. And a massive dose is very lethal. It is not, however, an especially desirable weapon, both because the spores persist for years after use and because the persons may not die immediately.

"This suggests," continued the federation, "that Soviet motivation for violating the treaty could not, or should not, have been very high."

Soviet scientists should strive to get out the facts, said the federation, to lessen the risk that the 113 nations who foreswore biological warfare by signing the treaty will pursue the capability.