The National Council on the Arts began its quarterly meeting here yesterday as part pep rally, part defense of the National Endowment for the Arts -- the agency it advises -- which is now threatened with 50 percent budget cuts, the first in its 15-year history.

"We have to make the strongest case for the least reductions," said Council member and folk singer/actor Theodore Bikel. "We don't fund organizations, we seed them. We give them about 10 percent of their budgets -- if that. We disseminate the arts across the width and breadth of this country, and this is a huge country."

At a meeting marked by the appearances of a powerful Democratic congressman and aninfluential Republican transition leader, what the Council wanted to know was whether or not the Reagan administration would adopt the 50 percent cut -- $88 million -- in the NEA budget proposed by David Stockman's Office of Management and Budget.

Robert S. Carter, who headed the Reagan transition team for NEA, told the Council at yesterday morning's closed session that the president and White House staff had just been examining the proposed budgets for the NEA and a variety of other agencies.

Carter would not speculate on how much of a cut Reagan would finally recommend. "The Arts Endowment should assume they're going to get some cuts and just hope they don't get hurt too much. As I told [the Council] this morning, Dave Stockman was originally for ablolishing the endowments. But then he proposed a 50 percent cut. At least he's moving in the right direction."

Carter said he expected Reagan to take budget papers, including those on the NEA, to Camp David with him this weekend for further consideration. Carter and others said they hoped they would learn the final proposed budget for the NEA on Tuesday.

"There have been telegrams, calls, messages of concern that have gotten to Reagan concerning the endowment cuts," said Carter after his talk at the Council. "Key members of Congress and governors have been meeting with him last week. I'm sure some of them have been talking about the endowment. When Bill Miliken, the governor of Michigan, met with the president this week, I'm sure he didn't waste any time getting to that issue. And I understand Sid Yates [Democratic representative from Illinois] wrote Reagan a letter."

Carter said he had talked to presidential counselor Ed Meese "and other appropriate officials. I told them to take a good look at the endowment before they do anything."

Rep. Yates, the influential chairman of the House Appropriations subcommittee that approves the budgets of both the arts and the humanities endowments, made an unusual appearance yesterday to have a private lunch with the Council members.

"He said the ball is not in the Congress's court right now," said one Council member after the lunch. "He told us we ought to proceed at full speed until we know what's what. We shouldn't be intimidated by looming cuts. sTo me, that means plan your programs as if you had all your money."

But the NEA plans a closed meeting with the Council and agency program heads to discuss priorities in the budget, since it is unlikely that the agency will receive the full $175 million that President Carter had proposed in his fiscal 1982 budget.

At least one NEA program -- which handles funds for state programs -- has begun a chart which shows the impact of cuts at several hypothetical percentages -- 10, 20, 30, 40, 50 percent.

"It's not very pretty," said one NEA official.

The Office of Federal-State Partnership administers the basic state operating grants -- funds given to state arts agencies (and in the District, to the D.C. Commission on the Arts) for grants to artists and arts groups. Congress has mandated that the NEA give at least 20 percent of its total budget to the states.

"Generally a large cut in the budget will work to the disadvantage of small or rural states where the portion the NEA gives is a large chunk of the state arts agency's budget," said Henry Putsch, director of the partnership office.

"if -- God forbid -- there's a 50 percent cut in the NEA's budget," said another endowment official, "our contribution to the D.C. Commission on the Arts would go from $303,000 this fiscal 1981 to $200,000 fiscal 1982."

NEA Chairman Livingston Biddle disputed the section of David Stockman's "black book" which argued that extensive federal funding for the arts had "resulted in a reduction in the historic role of private individual and corporate philanthropic support. . ."

"I think that, from the very outset, Congress envisioned the very role of the endowment as catalyst," said Biddle. "Corporate support for the arts has grown from $22 million in 1966 to more than $435 million today."

In the 10 years prior to the NEA's founding in 1965, Biddle said, philanthropic support for the arts grew only from $199 million to $205 million. pIn the 10 years after 1965, said Biddle, "that philanthropic support had increased to $2.7 billion."