The National Endowments for the Arts and Humanities reacted with "wait-and-see" attitudes toward yesterday's news reports that budget-cutters in the Office of Management and Budget had proposed 50-percent reductions in each agency's budget.

Throughout their 15-year history, both Endowments have enjoyed continuous increases in their budgets despite occasional debate over funding levels. "This town is political," said one NEA staffer. "People are used to this. Someone's just trying to run it up a flagpole and see what the reaction is. There's nothing much we can do but wait and see."

Both Endowments released similar statements stressing the "bipartisan support" they have received for their annual funding, now at $152 million for the NEH and $158 million for the NEA. "We have no comments on the news reports until we obtain information from the administration on its plans," read the NEH statement. The NEA said its staff had "received no official word regarding possible reductions in the budget."

On the Hill, some members of Congress took the opportunity to make their support for the arts clear.

"I don't believe President Reagan himself, who has feelings for the arts, would accept 50-percent cuts," said Rep. Fred Richmond (D-N.Y.), the founder of the recently formed House arts caucus."The average member of Congress has various art forms in his district that are pursued by middle-class people who are articulate, voting and capable of getting their opinions across to their congressman."

Sen. Howard Metzenbaum (D-Ohio) -- who yesterday sent out a letter asking his colleagues to join him and Sen. Claiborne (D-R.I.) in creating an informal organization called Concerned Senators for the Arts -- also was skeptical about congressional support for the cuts. "We're really talking about a very modest amount of money," he said.

Richmond said he thought the proposed cuts were a "trail balloon." "That's all it is," he said. "If it weren't, it wouldn't be coming from David Stockman, would it?"

"I don't think anyone could talk abut specific cuts until Reagan's economic plan is announced Feb. 18," said Diana Rice, assistant to David Stockman, director of the Office of Management and Budget. No one in the OMB would comment on the proposed cuts.