Arts and humanities advocates are prepared to fight President Reagan's fiscal 1983 budget requests for the National Endowments for the Arts and the Humanities much the same way they fought his fiscal 1982 request that funds be cut in half.

The Reagan budget message that goes to Congress Monday is expected to contain a request for $100 million for the National Endowment for the Arts and $96 million for the National Endowment for the Humanities. Currently, the NEA is funded at $143 million and the NEH at $130 million. Both figures represent substantial increases over the Reagan proposals: Initially, last year Reagan requested $88 million for NEA and $85 million for NEH.

Lobbyists this year admit that they are fatigued and unsure about whether Congress will come through for the endowments the way it did last year.

"It's going to be a tough year," said Anne Murphy, director of the American Arts Alliance. "Tougher than last. People did their best. They made all the arguments they could make. People are tired. I think Congress is tired. They went through all this last year, too . . . We'll fight the cuts . But it's almost too early to tell how."

Deborah Cooney, the editor of the Humanities Report -- a magazine published by the American Association for the Advancement of the Humanities -- echoed Murphy's words. "Everybody's tired," Cooney said, "but that doesn't mean we'll give up."

In Congress, Rep. Sidney Yates (D-Ill.), the chairman of the House Appropriations Subcommittee on the Interior and Related Agencies, is expected by arts advocates to pick up the fight where he left off last year. "Sid is undoubtedly one of our staunchest allies," said Anne Murphy. "There's no question that he will continue to carry the flag. But he's one out of a larger body. There just are so many variables."

Said Yates, "I think we have to see what Mr. Hodsoll NEA chair Frank Hodsoll wants." He said he would also have to hear the testimony of representatives of arts groups and state arts agencies. "We have to listen to what they say their needs are. I'd rather not speculate. I think it's better to wait and hear the facts before we decide how much money there should be."

Rep. Frederick Richmond (D-N.Y.) said he will fight the budget request. "We have every intention of at least working toward a budget no less than the current one," said Richmond, the founder of the Congressional Arts Caucus. "And that's a bare minimum . . . In this climate, anything's difficult. But I hope this Congress doesn't just lie down and give up everything good that has been worked for. The endowments have been so good at generating more funds than the taxpayers give them."

Arts and humanities organizations are already contacting their memberships and discussing how to proceed. "We'll expand our Washington coverage," said Cooney, "with the explicit message of 'Write your congressman.' "

"We've had preliminary discussions with museum people," said Moira Egan, director of the National Humanities Alliance, the organization that last year assembled such luminaries as prize-winning author Barbara Tuchman and actor Ossie Davis to testify before Congress on behalf of an increased NEH budget. This year, Congress will hear public witnesses on behalf of the endowments on April 5 and 6.

"A lot of the arguments we used last year are still valid," said Murphy, who gave an example: "The input of the federal dollar is important in generating more funds."

This year, that federal dollar is even more urgently needed, according to Murphy. "What I'm finding is that the money is not there in the private sector. The giving pie is not increasing, but the number of people seeking a piece has increased dramatically."

The notion that the private sector will pick up where the federal government leaves off is central to the way President Reagan and his new endowments chairmen see federal funding for the arts and the humanities.

"If the budget is $96 million, I can support it," said William Bennett, the new NEH chairman, who raised funds for the National Humanities Center. "I don't know what all the little numbers add up to yet. But $96 million seems like a lot of money to me." Bennett plans to meet with foundation directors tomorrow in New York to talk about humanities projects they are supporting.

"Livingston Biddle the Carter appointee in the NEA post was associated with higher budgets," said one NEA official. "Obviously the tone and texture of this endowment is different. The place is not as shocked by a $100 million budget as they were by $88 million. People really didn't expect $88 million last year."

"I think the arts community feels, 'We'll win this one in Congress,' " said the NEA official. "But the degree to which they'll win the fight -- $119 million or $134 million or what -- is uncertain."