WASHINGTON--The Senate's Democratic and Republican leaders agreed yesterday that enough time remains to approve the medium-range missile treaty before President Reagan's summit meeting next week.

They said that passage would be possible as long as the Senate votes to halt debate by conservative Republicans, a process begaun yesterday by Senate Majority Leader Robert Byrd (D-W.Va.) who petitioned to end discussion. That measure, known as a cloture vote, cannot come up for a vote before Thursday.

"It's conceivable that we could finish the work on the treaty by Friday or Saturday," Byrd told reporters after a White House meeting with Reagan to discuss the May 29-June 2 summit-between the president and Soviet leader Mikhail S. Gorbachev.

Senate Minority Leader Bob Dole (R-Kan.) agreed with Byrd that time remains before the summit to ratify the Intermediate-range Nuclear Forces treaty. "We can make it if we start staying in late and we file cloture today," he told reporters.

A successful cloture motion, which would limit debate, requires 60 votes. Far more than 60 senators have supported the treaty in a series of early-round test votes. Approval of a cloture motion Thursday would begin a 30-hour clock for debate, meaning a vote on the treaty could occur Friday.

Byrd said he wants the Senate to act before Reagan meets Gorbachev. "I think the president's hand would be strengthened there and I think it would be in the interests of our own country to have the president with the instruments of ratification."

GOP conservatives opposing the pact have used Senate rules, which are designed to protect the minority, to delay a vote on the pact signed Dec. 8 by Reagan and Gorbachev.

Reagan, setting the stage for the summit, said yesterday he hoped to conclude a treaty to cut long-range nuclear arsenals before his term expires in eight months. But the president acknowledged that might not be possible.

"It is the requirements of a good treaty and not some arbitrary deadline that will determine the timetable," Reagan said in an address beamed across Europe on the U.S. Information Agency's "Worldnet" satellite service. The speech was taped Monday in the Oval Office.

The INF treaty requires the elimination within three years of all U.S. and Soviet missiles with a range of 300 miles to 3,400 miles.

When the Senate finally votes on the pact, ratification is assured, Dole noted, because only 67 votes are required. "The question is how many votes are going to be for it," he said. "Is it going to be 94, 95, 92? It's not even close."

Sen. Jesse Helms (R-N.C.), the chief opponent, refused to mute his criticism.

Helms noted his long support of Reagan, but said, "I think he's wrong on this treaty, I think he's been misled, I think he's been misguided and my conscience will not allow me not to pursue the obvious defects of this treaty."