National Endowment for the Humanities chairman William Bennett not only strongly endorsed President Reagan's proposed NEH budget cuts during testimony before a House subcommittee yesterday, but refused--citing an administration order--to tell the subcommittee chairman what he would do with more funds if Congress appropriated them.

"Suppose Congress were, in its wisdom, to provide more funds than asked for? Suppose it went up to $110 million or $115 million?" asked Rep. Sidney Yates (D-Ill.), chairman of the House Appropriations subcommittee on the interior and a longtime supporter of the arts. Reagan has proposed a $96 million budget for the next fiscal year, down from this year's $130 million budget.

"I can't come out against wisdom," said Bennett to laughter.

"Would you favor an increase? Would it help the humanities?" asked Yates.

"No, I would not favor it," said Bennett. "In answer to the second question, it depends on how we would spend it."

"Would you be able to spend it?" asked Yates.

"I've been ordered not to speculate," said Bennett.

When Yates asked if the NEH would be able to prepare a possible budget at the $110 million level, Bennett said he would "have to consult with OMB about whether it was appropriate."

Bennett's reason, as Yates knew, was a March 29 memo from David Stockman, director of the Office of Management and Budget, to executive department heads, which reads: "In responding to specific questions on program and appropriation requests, witnesses will refrain from providing plans for the use of appropriations that exceed the president's request." An amendment to the memo, issued by the Department of Energy, says that includes "responses to questions raised by Members of Congress or their staffs . . . "

Said Yates, "It doesn't make sense for you not to be able to advise us about where extra money should be spent, because you're right there. It's kind of interesting--Mr. Stockman doesn't tell you not to say where you think funds should be cut."

After the hearing, Yates called the memo "a real stumbling block to congressional hearings--a real barrier . . . it prevents congressional committees from obtaining information needed for recommending appropriate funding for the agencies."

Bennett testified that the NEH would not be "seriously hurt" by a reduction to $96 million in budget funds. "No one should ever think that the support for the humanities activities in the country is centered only in Washington," Bennett said outside the hearing. NEH funding "can't be more than 1 percent of all the funding."