The United States said today that Soviet authorities in recent months had sharply reduced the level of microwave radiation beamed at the American Embassy in Moscow. But in its first detailed public account of the situation the State Department nonetheless rebuked the Russians for continuing the radiation even at the current insignificant level. It said this showed a lack of concern for living and working conditions of our people in Moscow." Robert L. Funseth, the department spokesman ... refused to comment on why the Soviet Union was beaming the rays, a practice that officials have said began about 16 years ago. Soviet officials have justified the beams as necessary to curtail American electronic listening devices on the roof of upper floors of the embassy building. American officials have privately conceded that these devices exist to monitor Soviet radio and telephone transmissions. They have also said that the monitoring effort was being impaired by the jamming waves. What has irritated American officials was that the Soviet Embassy [in] Washington also carries out similar interceptions ... has not been subject to the countermeasures because of concern for Americans working in the area. The beaming of radiation against the embassy in Moscow was known only to a few American officials until last February when Ambassador Walter J. Stoessel Jr. briefed his staff on the situation ... because State Department medical officers feared that the radiation might pose a health hazard.