On a sage-covered plain east of the Rattlesnake Hills, a towering drill rig stands ready to probe almost a mile down into some of the thickest lava deposits in the world to investigate their suitability as a repository for the nation's deadly nuclear wastes.

The massive derrick, brought here from western Oklahoma, where it drilled the two deepest holes in the world in search of natural gas, was all set to begin sinking an exploratory shaft into the basalts of the Columbia River plateau Feb. 16.

But the huge orange rig sits idle--a $10,000-a-day monument to the complex technical, political and social problems associated with picking America's first site for burial of radioactive wastes that will remain highly toxic to man for centuries.

The Energy Department, which must conduct a detailed exploration of three possible locations before a final selection is made in March, 1987, tried to get a head start here at the Hanford nuclear reservation, a 570-square-mile site used by the government since 1943 to produce plutonium for nuclear weapons.

On the basis of studies begun here in the late 1970s, the Energy Department last year picked what experts concluded would be the optimum Hanford location for an exploratory shaft, published a site characterization report and a draft environmental assessment, and prepared to drill.

But before the huge drill bit could begin chewing into the rock, the Energy Department ran into a buzz saw of criticism from the Nuclear Regulatory Commission, the U.S. Geological Survey, the state of Washington and the Yakima Indian Nation for trying to move too fast over uncharted ground.

Faced with the certainty that it would be sued if it tried to proceed, the Energy Department backed off, and the Hanford site is now on the same timetable as the eight locations in five other states that are candidates to be the first waste repository.

"Unfortunately, there is no technical precedent for a geological repository for high-level nuclear waste," said David Pentz, a vice president of Golder Associates, which has been advising the Nuclear Regulatory Commission on geologic disposal. "It is different from a mine or indeed any other nuclear facility."

Many scientists suggest that because of the "pioneering" nature of designing and predicting the performance of a nuclear waste repository, it may take years longer than the Energy Department believes to address the questions involved.

The major issue here concerns how water flows through the rock and whether water could come into contact with nuclear waste and return to the environment, where it would pose a health threat.

In the site characterization report for Hanford, the Energy Department said its studies "unanimously agree that the minimum travel time from the repository to the accessible environment under natural, preemplacement conditions is likely to be on the order of 10,000 years or longer."

But the NRC, which made studies using the same data, concluded that the range of possible travel times was "from 20 years to 43,547 years."

The U.S. Geological Survey criticized other aspects of the Energy Department's report on its preliminary studies as "overstated, misleading or simply incorrect," and said the report did not "adequately point out the seriousness of potential weaknesses of the site."

The National Academy of Sciences, in its new report on geologic repositories, said the basalt being considered for the Hanford project "is physically much less favorable than some other repository rock types."

In view of these criticisms, the Energy Department has come under fire from groups in Washington state for both the quality of the work here and selective presentation of its studies' results.

"What is most disturbing is the implication that those engaged in the Hanford site review seem to perceive their mission as one of painting as rosy a picture as possible to assure that the site is developed as a repository," Rep. Morris K. Udall (D-Ariz.) said at a hearing on Capitol Hill yesterday.

Robert L. Morgan, acting project director for the Energy Department's waste program, also appeared at the hearing and accepted most of the criticisms directed at the Hanford work as "valid and constructive." He indicated a better performance could be expected in the future.