The struggle between the Reagan administration and Senate Democrats over treaty-making powers deepened yesterday as key Democrats indicated they plan to force a showdown over the issue in connection with the the new U.S.-Soviet treaty to eliminate intermediate-range nuclear forces (INF).

Senate Majority Whip Alan Cranston (D-Calif.) said he intends to try to add a treaty condition to prevent reinterpretation of treaties without Senate consent, and Armed Services Committee Chairman Sam Nunn (D-Ga.) said "it looks as of now that some reservation may be necessary."

Several Republicans vowed to fight such a move, and warned it could delay or jeopardize Senate approval of the treaty. Sen. Dan Quayle (R-Ind.) said he may retaliate with a proposal aimed at binding the Soviets as well as the United States to accept testimony during ratification hearings as the legally binding interpretation of the INF Treaty, a move that could require renegotiation.

Yesterday's crossfire indicated that attempts last week by Secretary of State George P. Shultz to calm waters in the Senate did not fully succeed. Democrats said he had satisfied some but not all of their concerns, while some conservative Republicans complained that Shultz should have made no concessions. {Related story, Page A17.}

At issue beneath the surface is the administration's attempt to reinterpret the 1972 Antiballistic Missile Treaty (ABM) to permit advanced testing of Strategic Defense Initiative (SDI) technology. Democrats want to use the INF debate to set precedents that would block such a "broad" reading, while Republican conservatives are pushing to protect a broad interpretation to pave the way for an early start for SDI deployments.

While Shultz agreed with Democratic leaders' contention that administration testimony during ratification hearings would be considered authoritative, his assurances could not bind future administrations, Nunn said. So the Senate may have to do so as part of its resolution of ratification, he added.

This appeared to put him on the same track as Sen. Joseph R. Biden Jr. (D-Del.), who has been pushing for a treaty reservation to rule out any future reinterpretations without Senate consent. With Biden currently hospitalized as a result of surgery, Cranston said he would push for adoption of the reservation.

However, he indicated he would "take another tack" if it appeared the proposal would jeopardize the treaty. He said he did not believe opposition to the reservation is serious.

But Sen. Pete Wilson (R-Calif.), an SDI proponent who had objected to Shultz's concessions, said a Biden-type reservation could jeopardize the two-thirds vote of the Senate needed for ratification.

Meanwhile, Nunn and Senate Majority Leader Robert C. Byrd (D-W.Va.) said they concluded from meetings with Western European leaders that, while North Atlantic Treaty Organization countries generally support modernizing battlefield nuclear weapons, there is no consensus yet on how to proceed.

"I do think there is a consensus for the modernization of short-range nuclear weapons," Nunn said, but no agreement yet on which weapons to build.