The U.S.-Soviet medium-range missile treaty has a better than even chance of winning Senate ratification before President Reagan meets with Soviet leader Mikhail S. Gorbachev in Moscow later this month, two senators said Tuesday.

"I'd say a 60-40 chance at least, maybe better," Sen. Sam Nunn, D-Ga., chairman of the Senate Armed Services Committee, said on NBC-TV's "Today" program."I would say 75-25 to the good," added Sen. Richard Lugar, R-Ind., a member of the Foreign Relations Committee.

The remaining obstacles to beginning floor debate sometime Tuesday were removed Monday, ending a process of

intense scrutiny that began soon after the treaty was signed in early December.

Three Senate committees told Senate majority leader Robert C. Byrd, D-W.Va., that last week's agreement in Geneva between Secretary of State George P. Shultz and Soviet Foreign Minister Eduard Shevardnadze satisfactorily resolved disputes about how to implement the treaty's on-site inspection provisions.

Nunn and Lugar said they have felt considerable pressure to ratify the Intermediate-range Nuclear Forces or INF treaty before the upcoming summit. However, Nunn said INF ratification before the superpower summit will have little effect in producing a U.S.-Soviet agreement on strategic arms.

"I don't visualize a START treaty coming out of the summit, no matter what the Senate does on INF," Nunn said. "I think we will continue to discuss START and try to make progress."

The INF treaty, signed at the White House on Dec. 8 by Reagan and Gorbachev, would require the elimination of all U.S. and Soviet missiles with a range of between 300 miles and 3,400 miles.

The decision to begin Senate floor action on the pact followed testimony in which Shultz said that in the Geneva talks, "we got what we needed and wanted."

Shultz said that included both the on-site inspection and a Soviet agreement that medium-range weapons using such futuristic technology as particle beam generators are banned by the treaty.

Both issues had delayed consideration of the treaty on the Senate floor with Byrd vowing not to schedule action until they were resolved.

Byrd said Monday that he had been assured by the Senate Foreign Relations, Intelligence and Armed Services committees that the problems had in fact been resolved.

"I feel satisfied that we're justified in taking up the treaty and I plan to do so," Byrd said.

Byrd said he hoped the treaty could be ratified by the May 29 opening of the Moscow summit but could not guarantee it.

Finishing the treaty by the time of the summit will depend on the nature of the debate and the number of amendments that are offered, he said.

Byrd said he plans to call up the treaty and stay on it but noted there may be some roadblocks. For example, he said that if President Reagan vetoes the trade bill, an attempt to override that action would take precedence over the treaty and would interrupt its consideration.