Senate Majority Leader George Mitchell said Saturday that the United Nations' decision to move a General Assembly meeting to Geneva was "a regrettable action."

Mitchell, D-Maine, commented in an interview a day after the U.N. voted to move the session to permit Yasser Arafat, chairman of the Palestine Liberation Organization, to speak to the General Assembly.The decision came after Secretary of State George Shultz barred Arafat from entering the United States, home of the U.N., because of what Shultz said was Arafat's support for terrorism.

"I think it's a regrettable action," Mitchell said of the U.N. decision. "It represents, for the United States, an isolation and will of course remove the debate from the United States at least for a period of time."

Mitchell said Shultz's decision "was clear and concise and well-taken."

As for the effort to broker a peace treaty the Mideast, Mitchell said, "I don't think it derails the peace process. It's been very diffuclt of course. There have been a number of obstacles over time, and we're going to work to continue to do what we can to encourage direct negotiations between the parties."

Earlier, in his response to President Reagan's weekly radio address, Mitchell pledged to cooperate with President-elect George Bush when Bush takes office next month.

Noting that the White House will be controlled by Republicans while Democrats run Congress, Mitchell said, "power will be shared. Some say this renders our government impotent. That could happen. But it doesn't have to.

"The larger objective is to provide to our people the greatest possible individual liberty and economic opportunity," he said.

"It is our joint responsibility - president and Congress - to meet the challenges facing our nation in the way that best serves all our people," he said.

"Of course, we have differences. And there will be disagreements. It wouldn't be democracy if we didn't."