Water supplies of hundreds of communities in 15 western states may be dangerous for long-term use because of low-level radiation from uranium, according to federal officials here.

The contamination, formerly believed to be harmless, has increased so dramatically in recent years that the Environmental Protection Agency estimates some residents here could be getting as much as 60 times the normal yearly amount of alpha radition - a low-level variety that occurs naturally in food and water. The agency's review of a small community's water here could lead to establishment, for the first time, of a standard for radiation pollution of drinking water.

"It's of national significance," said Paul B. Smith, EPA's regional director of radiation programs in Denver. "You're dealing with the generic question of radiation in drinking water in the whole West."

The agency recommended "prompt control measures" to reduce alpha radiation levels in the Denver-area water, and Smith said that similar pollution was likely in other western communities, too.

He recommended an extensive reevaluation of uranium radiation in drinking water in 15 western states. If the informal guidelines advised for the Denver water are applied elsewhere, he said, "some supplies could be rendered undrinkable."

The study of one Denver suburb's water system was sought by Colorado's health department last spring, after many of the area's 7,500 water customers became concerned about possible effects from low-level uranium radiation.

The suburb, Fairmount, gets its water from Upper Long Lake, fed by Ralston Creek, into which the Cotter Corp.'s Golden uranium mine - the state's largest - dumps its wastes. Residents are especially sensitive to atomic-age hazards; they live seven miles downwind of the Rocky Flats nuclear weapons plant.

For 10 years, the state health department has recorded increasingly high alpha radiation levels in drinking water - a result, EPA says, of discharges from the mine. But Colorado, like most states, doesn't include uranium-caused alpha radiation in its pollution standards.The federal Safe Drinking Water Act of 1974 doesn't require such controls either.

Alpha radiation is the least penetrating of the three common types of radiation. It can be stopped by a piece of paper, but can be harmful to plants, animals and humans when it enters the body.

EPA said the uranium-laden Fairmount water results in an annual alpha radiation dose to bone cells of 3,000 millirems - roughly 60 times what the average American receives from naturally occurring radiation in food and water.

Historically, it has been believed that the chemical toxicity of uranium in drinking water, also is unregulated by federal standards, would cause problems to the kidneys before radiation would affect the body.

But in a letter about the Fairmount contamination to Dr. Frank Traylor, executive director of the state health department, Dr. William L. Lappenbusch of the EPA's Office of Drinking Water in Washington recommended that doses of uranium radiation be limited to 10 picocuries per liter daily.

That would result in an average daily consumption of roughly 20 picocuries daily. Alpha radiation levels as high as 500 picocuries per liter have been measured in the Fairmount system's water.

In suggesting the guidelines for the Colorado water supply, Lappenbusch cited a report issued by National Academy of Science's biological effect of ionizing radiation committee, which has been studying the possibility that low-level radiation may be more dangerous than originally thought.

The national drinking water standards are undergoing revision but no decision has been made yet as to whether uranium-caused radiation will be regulated, an EPA spokesman here said.

Because large populations are needed to measure accurately the effects of a radiation source, officials say they don't know what health effects - if any - the Fairmount radiation is causing. But Lappenbusch has said that the suggested guidelines for uranium radiation dosage would be expected to result in three additional bone cancer deaths in 1 million persons who drank the water over a lifetime.

Smith said that children are particularly susceptible to radiation because it may accumulate in the youngsters' evolving skeletal systems.