Senate Armed Services Committee members expressed "astonishment" and "bewilderment" for the second day yesterday over Paul C. Warnke's repeated denials that he has changed his key arms control positions.

Sen. Henry M. Jackson (D-Wash.) accused Warnke, President Carter's nominee to head the Arms Control and Disarmament Agency and be the chief U.S. atrategic arms negotiator with the Soviets, of using "needle-threading loopholes" to avoid admitting a change.

Three conservative Republican members of the Senate Armed Services Committee told Warnke they could not support him.

Sens. Barry Goldwater (Ariz.) and William L. Scott (Va.) said Warnke was too ready to let down America's guard.

TGoldwater and Sen. Jake Garn (Utah) made it clear that their disapproval of Carter's policy on defense is behind their decision to oppose Warnke.

Scott told Warnke, "I wonder if you couldn't better serve your government as head of the Peace Corps."

Chairman John C. Stennis announced at the end of Warnke's second day on the stand that the committee will hold one further hearing, with four witnesses from the public, Monday. Two are to be Warnke supporters and two opponents.

Stennis said it was not decided whether or not his committee, which has no jurisdiction over the nomination, would take a vote on Warnke. It is clear that majority ofthe committee, perhaps two-thirds, would oppose him.

Sen. Gary W. Hart (D-Colo,), one of Warnke's supporters, said taking a vote would set a bad precedent and be an unwarranted instrusion into the Foreign Relations overwhelmingly approved Warnke Tuesday.

The nomination will probably reach the floor late next week. Warnke supporters believe the Armed Services hearings have not added to the slightly under 30 votes they expect to be cast against Warnke.

The administration has given Warnke full and active support, including telephone calls from Carter to several senators.

Jackson sought to develop a case that Warnke has changed his arms control and weapons procurement opinions only for his testimony before the Senate since his Feb. 4 nomination.

He asked a series on nine lenghty questions and requested Warnke to answer each by submitting for the hearing record evidence that what Warnke told the committee about the need for equality of U.S. and Soviet strategic arsenals and the seriousness of the Soviet threat are not new positions for him.

"That's what I believe this whole hearing is about," Jackson said.

Warnke's opponents intend to fight the nomination on the Senate floor, apparently drawing upon the record the Armed Services Committee has built.

Sen. Jesse A. Helms (R-N.C.) indicated earlier this week that he was considering a filibuster against the Warnke nomination.

Sen. Thomas J. McIntyre (D-N.H.) led the support for Warnke yesterday, declaring: "We're on our way to Dommsday," unless the arms race is halted.

All the talk of 20 million dead on one side and 40 million dead on the other side, that's "insanity, that's all it is," McIntyre said.