The Soviet nuclear disaster may threaten for weeks the lives of those exposed locally to severe radiation doses and may pose a lifetime threat of cancer to many others in the vicinity of the accident.

Radiation blown worldwide in the atmosphere, however, poses no measurable health risk in the United States, American experts said yesterday.

"Based on what we have now, it will pose no hazard," an Environmental Protection Agency spokesman said, adding that no increase in radiation levels has been monitored in this country.

Air filters from 67 monitoring sites nationwide were sent yesterday to an EPA laboratory in Montgomery, Ala., which is checking such reports daily, rather than the usual twice weekly, during the current alert.

International monitoring also has increased, with eastern and northern European countries reporting more radioactivity in air and water.

Meanwhile, the International Physicians for the Prevention of Nuclear War and its U.S. chapter, Physicians for Social Responsibility, cabled concern and offers of help to the Kremlin's chief physician, Dr. Yevgeni Chazov.

Chazov, who shared the 1985 Nobel Peace Prize with IPPNW copresident Dr. Bernard Lown, sent Lown a cable declining the offer, United Press International reported. "All questions are being effectively resolved and at the moment there is no need of help on behalf of the international medical community," Chazov said.

Predictions about possible health consequences of radiation exposure are based on decades of work, careful followup of 60,000 irradiated survivors of the 1945 atomic bombings of Hiroshima and Nagasaki and numerous studies of purposeful or accidental medical and occupational exposure to radiation.

Experts cautioned that sketchy information from the Soviet site makes it difficult to estimate potential health consequences in that country.

They said the disaster's dimensions will depend on the amount and type of radiation released, how long it was released, local weather conditions and the amount of time needed to evacuate victims.

Soviet disclosures yesterday that at least 197 persons have been hospitalized, in addition to the two deaths reported earlier, provided few clues about their illnesses.

U.S. experts said those hospitalized could have suffered physical damage from an explosion or fire or may be only the first few of many who will suffer radiation sickness.

Short-term radiation damage can show up within minutes or weeks after exposure, while cancers and genetic damage may not appear for decades.

Radiation damage occurs when ionized rays penetrate human tissue. Cells most susceptible to damage are rapid dividers and include bone-marrow tissues that produce blood cells and cells lining the intestines.

Exposure levels are measured in units known as rads or rems. A low level of natural "background" radiation, averaging about one-tenth of a rem, usually exists in the environment.

Numerous texts have reported potential short-term effects of exposure on humans, including:

*At the highest levels of whole-body exposure to radiation, measured in thousands of rads, the central nervous system is virtually destroyed, leading to disorientation, vomiting, convulsions and possible coma. Death usually occurs within hours.

That this would occur from a nuclear power plant accident, however severe, is "pretty inconceivable," according to Dr. William H. Ellett, a radiation expert at the National Academy of Sciences.

*Whole-body doses of 500 rads or greater can cause massive destruction of the intestines. Symptoms, generally appearing within three to five days, include nausea, vomiting and severe diarrhea, and frequently lead to death.

*One who survives the intestinal problem would be susceptible to "bone-marrow syndrome." Whole-body radiation of a few hundred rads or more can stop cell production in the marrow, ending production of red blood cells and white blood cells needed for fighting infection.

Acute effects may not appear for a month or two, Ellett said.

It is difficult to estimate how far from the Soviet nuclear plant the most severe short-term effects would occur, experts said.

Joe Logsdon, a health physicist in EPA's office of radiation programs, said yesterday that government worst-case scenarios of such an accident in this country have estimated that severe radiation exposure could mean a 50 percent chance of death within 60 days to individuals living within about 20 miles.

He said these estimates, prepared by the EPA and the Nuclear Regulatory Commission, have suggested that from 30 to 50 miles away, the chance of long-term health hazards, particularly cancer, increases. He emphasized that it is impossible to "put a line" at which the latter hazards end.

Cancer risks are posed by several types of radioisotopes, with radioactive iodine a particular hazard to milk, fresh food and water. It can concentrate in the thyroid gland, leading to short-term dysfunction and cancer. Thyroid effects can be prevented by a blocking agent called potassium iodide.

Other radioisotopes, particularly varieties of cesium and strontium that can stay in the environment for decades, may increase long-term risk of leukemia and other cancers. Leukemia may appear three or four years after exposure, Ellett said, while other cancers may not develop for at least a decade.