Senate Majority Leader Robert Byrd, D-W.Va., said Thursday the U.S.-Soviet medium-range missile treaty could be approved before President Reagan leaves for Moscow next Wednesday.

"If only the legitimate and serious points of order and amendments are called up, this treaty can be approved in time for the president to take it with him to the summit," Byrd, D-W.Va., told reporters.The Senate voted 91-6 Wednesday to reject the first conservative attack on the treaty. That was a point of order raised by Sen. Jesse Helms, R-N.C., who claimed Soviet leader Mikhail S. Gorbachev wasn't authorized to sign the pact and the Senate therefore should not ratify it.

"The first vote would indicate the Senate did not think it was a serious point. I did not think it was," said Byrd.

Republican Leader Bob Dole, R-Kan., said, "we need to get some action . . . We need to have the debate, have the vote, and move on."

"I feel a particular responsibility in this instance" because there is a Republican in the White House,and Republican conservatives are the chief critics of the treaty, Dole said.

"The burden is on the Republicans to move this along," said Dole, noting that the only proposed amendments have been spelled out by members of his party.

"Maybe we could even get lucky and finish this by next Tuesday or Wednesday," said Dole. "I hope we continue to expedite this process."

Reagan leaves Wednesday for his Moscow summit meeting with Gorbachev and he has said he hopes he take a ratified treaty with him.

After the vote late Wednesday, Dole said, "I think the vote we've just had is an indication of the strong support we have for this treaty. Let's get on with it."

Sen. James Exon, D-Neb., agreed with Dole. "Let's do our work. Let's not fool around, which I think we are doing to a large extent on the amendment that was just defeated. . . . I don't know what benefit there is in waiting until after the summit begins to ratify this treaty."

"There is no cause for further, untimely delay," said Exon.

Sen. Robert Stafford, R-Vt., said "the American people want the president to have a ratified treaty in his briefcase when he meets" Gorbachev.

The Intermediate-range Nuclear Forces treaty, signed Dec. 8 by Reagan and Gorbachev, calls for the elimination of all missiles with a range of 300 miles to 3,400 miles.