House-Senate conferees for the Interior appropriations bill yesterday approved a budget of $149 million for the National Endowment for the Arts and a budget of $136 million for the National Endowment for the Humanities.

These figures are substantial gains over President Reagan's recommendation that the fiscal 1982 budgets of both agencies be cut in half. The administration proposed $88 million for the NEA and $85 million for the NEH.

The appropriations bill containing the endowments' funds must still be approved by the House and Senate. "If the $149 million figure passes," said outgoing NEA chairman Livingston Biddle, "it will require some minor amendments to our programs, but we could continue pretty much the way we have been." Biddle called the conferees' decision "a terrific tribute to Sid Yates," the Democrat who chairs the House Appropriations subcommittee on the interior.

Frank Hodsoll, Reagan's nominee for the NEA chair, had not officially heard about the conference decision early yesterday evening. "I've asked my staff to check into it. I've got to see what has happened before I can say any more." The Senate confirmation hearing on Hodsoll is scheduled to begin at 11 a.m. tomorrow.

At this point, neither agency can be certain of receiving the full recommended budgets.

"The conference figure will make it through the House easily," said one NEH official, "but the Senate may be a problem."

Even if both houses approve the bill, the president can veto it.