The Department of Energy has identified 50 sites in more than 20 states that were once used for nuclear research and development where radiation contamination problems still exist for the people there.

To clean up what one official yesterday described as "these unfavorable monuments to our nuclear programs," DOE has embarked on what could become a $250 million program.

Impetus for the cleanup came from what DOE officials said was increased awareness of the possible cancer risk form the low-level radiation emitted from sites once associated with the mining, processing and storing of uranuim, and the development of the atomic bomb and nuclear energy.

Last week, DOE released the names of 26 sites where decontamination work is needed to bring radiation levels down to those now considered safe.

In May, DOE Secretary James R. Schlesinger Jr. identified 24 abandoned uranium mill tailing sites where radioactive residues "pose a possible threat to the public through exposure to low levels of radioactivity." He requested legislation from Congress to meet that problem.

The Department of Health, Education and Welfare recently was named to coordinate a broad study of military and civilian personnel who took part in nuclear testing in the late 1950s and 1960s after a significant number exposed to one test turned up with leukemia.

On Sunday The Washington Post reported that HEW was taking a second look at the possible increase of leukemia and other medical effects among civilians living around nuclear testing sites in Nevada.

Dr William E. Mott, director of DOE's Division of Environment Control Technology, yesterday identified sites in Pennysylvania and New Jersey as presenting the most serious problems in the 26-site group.

At the Canonsburg (Pa.) Industrial Park, where uranium has been processed since the day of Madame Currie, according to Mott, radon gas given off by radioactive waste collected beneath the buildings creates exposure levels at times equal to "the maximum allowable for uranium miners."

Mott said "there is no question there is an increased of lung cancer" for any of the 120 current workers in the buildings who may have received those doses of radon gas over several years.

Mott could not say yesterday what remedial actions may be undertaken at Canonsburg, although a DOE spokesman suggested that, in some cases, decontamination or demolition of structures may be recommended.

DOE did an aerial survey of the Canonsburg area and found some new areas of radioactivity outside the immediate plant area where cleanup will have to take place.

At a landfill site near Canonsburg, 11,000 tons of radioactive material was dumped and covered over in 1957, according to Mott. Since the area is still radioactive and is used by hunters for target practice, Mott said additional cover must be placed on the contaminated material or the area will have to be closed to outsiders.

At Middlesex, N. J., DOE found high radioactivity levels at a Marine reserve training center that in the 1940s was used to process radioactive materials.

A nearby landfill site was found to exceed radiation limits and was fenced in almost two years ago.

An aerial radiation survey last month discovered another dumping site with radioactive materials that will require decontamination, according to Mott.

One DOE official said that today's problem areas were created by "the much looser way" radioactive materials were handled "in the early days."

The programs to clean up the old uranium mining sites and former processing and storage facilities were an effort "to get our house in order," he added.

A DOE study found that cleaning up the former mine sites could run to $125 million, but Mott yesterday said that figure could go higher depending on solutions adopted to handle the cleanup and the criteria set for acceptable residual radiation level in the soil.

Since there was no legal requirement for the past or present owners on the mulling sites to decontaminate the property, the Carter administration's legislation has proposed that the cost be shared by state and federal governments.

With the 26 former nuclear facilities, the federal government may end up paying the entire cost, according to Mott.

That amount also may run as highas $125 million, DOE sources said.