Senate Majority Leader Robert C. Byrd (D-W.Va.) predicted yesterday that the Senate will approve the new U.S.-Soviet nuclear weapons treaty without crippling restrictions and said he hopes for final action by mid-April.

But Byrd and others left open the possibility -- many said probability -- of reservations on issues such as verification and compliance, human rights guarantees, withdrawal of Soviet troops from Afghanistan and movement toward agreement on reduction of conventional military forces in Europe.

Some, including Byrd, also expressed concern about the treaty's impact on NATO and said they want to hear more from European leaders about their assessment of the implications for both conventional and nuclear capabilities within the alliance.

Byrd's prediction, made shortly before President Reagan and Soviet leader Mikhail Gorbachev signed the treaty to eliminate intermediate-range nuclear forces in Europe, appeared to reflect a mounting sense of optimism about the treaty's prospects in the Senate.

Byrd had previously avoided predicting the treaty's prospects and refused to set a target date for ratification. But after reading the pact's provisions, he told reporters that he does not foresee "anything . . . that would create serious problems for this treaty" and said "prospects are good" for ratification.

Some Republican conservatives continued to raise strong objections, however, and a few treaty proponents, including Majority Whip Alan Cranston (D-Calif.), cautioned that the treaty could be killed by approval of amendments or reservations that would be unacceptable to either the Reagan administration or the Soviet Union.

Sen. Malcolm Wallop (R-Wyo.), a leading conservative, said the Senate should consider "self-abrogating" language under which the United States would be freed from treaty obligations in the case of significant violations by the Soviets. Verification, he said, is useless "unless we can do something about it" when violations are found.

Cranston said the treaty could be doomed by proposals to require Soviet withdrawal from Afghanistan or Soviet compliance with previous treaty commitments before the INF pact could take effect.

Cranston said he sees no more than 23 senators who "might be inclined" to oppose the treaty, considerably short of the 34 needed to block a two-thirds vote necessary for Senate approval of a treaty. But he raised the possibility that a majority could support amendments that would become "killer" provisions.

"We have to be on guard against all such efforts and find ways to take legitimate concerns into account without wrecking the treaty," Cranston said.

Byrd's optimism about the treaty's prospects was echoed by Senate Armed Services Committee Chairman Sam Nunn (D-Ga.) and Sen. Ted Stevens (R-Alaska).

"I cannot conceive of this Senate refusing to approve this treaty" in a reasonable time and without crippling amendments, said Stevens. But he said he thought it would approve noncrippling amendments in a variety of areas, including human rights compliance and reduction of conventional force levels.

Stevens, who is the senior Republican on the Senate's arms-control observer group, said he is more concerned about delay that could impede negotiations on a broader strategic arms agreement. He said mid-April should be the "outside limit" for ratification.

"Barring something unforeseen, this treaty will go through," said Nunn. "The question is whether one or more reservations will require renegotiation" of the pact, he added.

Nunn has warned repeatedly that the administration itself is complicating prospects for ratification by its controversial position on treaty interpretation, made earlier to justify plans for Strategic Defense Initiative testing under a broad new reading of the 1972 Antiballistic Missile Treaty.

Nunn argued that testimony before congressional committees by State Department legal adviser Abraham D. Sofaer has cast doubt on any treaty interpretation that is not specifically spelled out in the treaty itself, its negotiating record or language approved by the Senate to clarify any ambiguities.

This issue has prompted Nunn and other Democratic leaders to demand the entire INF negotiating record. Moreover, unless the administration modifies its position on treaty interpretation, Nunn said, the Senate would have to clarify any ambiguities with specific reservations that, in turn, would have to be approved by the Soviets, a situation he described as an "absurdity . . . that makes ratification more difficult."

Nunn said he has asked to meet with Secretary of State George P. Shultz to attempt to get the administration to back off its position on treaty interpretation. "It would be better for the administration to take a few steps backward . . . . The last thing we need is for the Senate to be renegotiating a treaty," said Nunn.

Senate Minority Leader Robert J. Dole (R-Kan.), who has not yet taken a position on the treaty, appointed a GOP treaty coordinating group that includes moderates such as Sens. Richard G. Lugar (Ind.) and William S. Cohen (Maine) as well as conservatives such as Wallop and Sen. Jesse Helms (N.C.). It will be headed by Senate Minority Whip Alan K. Simpson (Wyo.).