The chairman of a federally funded scientific group urged yesterday that the government press ahead with an extensive survey of potential illness or deaths related to radioactive emissions in the 1940s from a factory producing plutonium for nuclear weapons in Hanford, Wash.

The recommendation by Dr. John Till, an independent radiation specialist, was based on the panel's discovery that 13,500 nearby residents were probably exposed to substantial emissions of radioiodine. The number included a small number of infants who probably received extremely high dosages considered almost certain to produce thyroid abnormalities or cancer.

Till told a news conference in Richland, a few miles from the shuttered Hanford plutonium processing facility, that the estimated radiation dosages exceeded those received by people living downwind from the principal site of U.S. nuclear weapons tests in Nevada. "These numbers are significant," he said. "I know of no other releases of this magnitude from any other U.S. facility."

All of the 13,500 people in the large-dose group "are at a higher risk of thyroid disease," Till said in an interview.

The disclosure by the panel, specifically formed to examine the Hanford emissions, unleashed a flood of complaints by activist groups and residents of Oregon and Washington. They charged that, in seeking to protect its nuclear weapons production efforts from political criticism and added expense, the government had deliberately withheld information about health risks at Hanford and should have begun a monitoring program years ago.

"I feel like they used us as guinea pigs, and I don't feel like they cared one iota what happened to us either, or to our families," Betty Perkes, whose family farms nearby, told the Associated Press.

While Hanford managers were aware of the magnitude of the emissions, they routinely said nearby residents were not at any health risk. Not until the threat of a lawsuit in 1986 forced public release of official radiation emissions data did the government acknowledge potential risks and agree to cooperate with an independent scientific group.

The group estimated that, while half the 270,000 nearby residents probably received small doses during the 1944-47 period of greatest emissions, about 13,500 people received more than 33 rad. About 1,200 infants may have had thyroid doses of between 15 and 650 rad, and a dozen or so infants in a particularly vulnerable downwind site may have received doses as high as 2,900 rad.

A rad is a measure of radiation dosage absorbed by human tissue and organs such as the thyroid, which plays a vital role in regulating metabolism. Federal health standards set in the 1950s called for limiting infant thyroid dosage to less than 0.5 rad per year, although adult workers today are permitted to receive up to 50 rad per year to the thyroid under international standards.

The Hanford area residents received "a lot of exposure, certainly more than we ever expected the general population would get," Warren K. Sinclair, president of the National Council on Radiation Protection, said. The highest estimated doses "certainly pose a risk of thyroid cancer," he said.

The principal route of exposure was through drinking milk from cows that had foraged on grasses contaminated by the radioiodine emissions, although some residents also ate contaminated vegetables or drank contaminated water from the nearby Columbia River, according to the report.

Till's group plans several years of additional study so it can estimate individual doses based on age, location, and other factors. A study of thyroid abnormalities in the surrounding population under the direction of the Seattle-based Fred Hutchinson Cancer Research Center will not be completed until late 1993.

A spokesman for the Department of Energy, which manages the Hanford complex, said the agency would have no immediate comment.