Senate Majority Leader Robert C. Byrd (D-W.Va.) predicted yesterday that Paul C. Warnke will be a "firm negotiator" and no "softie" in arms talks with the Russians. He said Warnke will be confirmed to the negotiator spot Wednesday with a minimum of 53 votes and possibly more than 60.

Byrd made the statement as the Senate, in its second day of sparsely attended debate on Warnke's dual nominations as negotiator and head of the Arms Control and Disarmament Agency, heard a warm defense of the nominee from Sens. Hubert H. Humphrey (D-Minn.) and Frank Church (D-Idaho).

Humphrey said Warnke had been right, not "soft," in opposing a go-ahead on the anit-ballistic missile, in urging a delay on putting multiple independently targetable re-entry vehicle (MIRV) warheads on U.S. missiles, and in questioning the B-1 bomber and the Trident nuclear submarine system. Moving ahead with MIRV unilaterally had "provoked a non-negotiable escalation on the part of the Russians." Humphrey said, and it would have been better to try to negotiate a no-MIRV agreement.

Church and Humphrey said that every time a big new weapons system is contemplated, it is desirable to try to negotiate a verifiable arms control agreement with Russia, rather than moving ahead unilaterally and thereby risking a Russian counter-move that leaves neither nation militarily ahead and costs billions.

A few hours after Byrd's statement on Warnke's prospects. Assistant Majority Leader Alan Cranston (D-Calif.) said his own estimate on Warnke right now as negotiator is "56 firm votes" with a possibility of going over 60.

Carter and Mondale have privately called about a quarter of the Senate, according to Senate sources.

Yesterday Warnke, in a letter to Armed Services Committee Chairman John C. Stennis (D-Miss.). denied charges made Friday by Sens. S. I. Hayakawa (R-Calif.) and Robert P. Griffin (R-Mich.) that he had misrep-presented a 1972 position on missile issues by deliberately omitting a comma from a statement sent ot senators recently explaining his past stands on armament matters.

Warnke said the 1972 statement had been made orally, at a hearing and he had no idea whether the transcript contained a comma put in by others or not. But he said he did know what he had meant, namely, that the Soviet lead in missile launchers in the 1972 arms agreement didn't give them any advantage because the United States at that time had MIRV and the Soviets didn't.

Warnke said he decidedly didn't mean that "no further development . . . in missile numbers and accuracy" on the part of the Soviets could threaten the United States - the meaning inferred by Griffin and Hayakawa.

Byrd, who announced Saturday he is voting for Warnke, along with Humphrey, Clifford P. Case (R-N.J.) and others said the idea that Warnke is discredited as a negotiator unless he gets a two-thirds vote, even though he only needs a majority, lacks validity.