RICHLAND, Wash. (AP) _ Hydrogen gas building up inside nuclear waste storage tanks at the Hanford nuclear reservation poses no risk to the public, the head of a congressional review group said Wednesday.

Two members of the Defense Nuclear Facilities Safety Board have spent the past two days at Hanford, conferring with officials for the U.S. Department of Energy about the tanks. Experts have said there is a chance the tanks could explode because of the hydrogen buildup.

''We don't believe there is any kind of risk to the public,'' said John Conway, chairman of the board, in a brief telephone interview.

Asked whether the issue has unnecessarily alarmed the public, as Energy Secretary James Watkins has contended, Conway said, ''The public has a reason to be concerned, unless it is explained properly to them.''

Conway spoke after he and board member Herbert Kouts had eight hours of briefings from DOE and experts.

Hanford manager Mike Lawrence announced last month that new findings indicated hydrogen was building up inside 20 of Hanford's 177 waste storage tanks. He said there was a low risk of the hydrogen catching fire or exploding.

Watkins subsequently criticized Lawrence before Congress for alarming the public over such a low risk.

Lawrence has said the problem is that hydrogen is trapped under the hard crust that forms at the top of the wastes, which are byproducts of the production of plutonium for nuclear weapons.

Scientists monitoring the wastes have watched them rise as much as 33 inches in past years, apparently the result of gases building up under the crust, DOE has said.

Conway said DOE officials must continue taking precautions to prevent the tanks from exploding. The Energy Department has stopped taking wastes in and out of the tanks, and reduced probing activities to prevent a spark from triggering an explosion.

''There are more things they'll have to do,'' Conway said, but did not elaborate.

The board needs additional information before making its recommendations to Watkins, and will visit Hanford again, he said.

The safety board was set up by Congress last year to monitor safety at DOE facilities.