The Senate Foreign Relations Committee Thursday rejected a move by Sen. Jesse Helms to require new intelligence studies of what Helms says are Soviet missiles unaccounted for by the U.S.-Soviet treaty on medium-range atomic weapons.

The committee voted 15-2 against Helms' amendment to the treaty which would have required President Reagan to certify the accuracy of the Soviet claims that there are 650 SS-20 missiles. The declared weapons will have to be destroyed after the treaty takes effect.Helms, R-N.C., argued that up to 300 more SS-20s are "hidden," and he cited Defense Intelligence Agency reports which he said support his claim.

But Sen. Daniel Evans, R-Wash., said, "I don't believe President Reagan would have signed this treaty" if he believed the Soviets had successfully hidden a large force of SS-20 missiles.

The vote was the latest decision in which the panel decided by large bipartisan majorities to reject attempts by Helms and Sen. Larry Pressler, R-S.D., another conservative critic, to change the treaty.

Sen. Claiborne Pell, D-R.I., chairman of the committee, said the panel was headed toward overwhelming approval of the pact.

"I would hope and I think that we will continue to show strong bipartisan support," said Pell after the panel voted by lopsided margins Wednesday to reject amendments by Helms and Pressler.

Helms had originally proposed 36 amendments and Pressler offered three more, despite appeals from the Reagan administration for the Senate to approve the treaty without changes.

After it became apparent he had few votes on his side, Helms said he planned to drop most of his amendments.

Pell announced that the committee will finish voting on all amendments by Tuesday afternoon next week and will then decide on the treaty itself.

When the measure finally reaches the floor, overwhelming approval is expected with no more than 10 to 12 of the 100 senators expected to vote against it. Ratification requires a two-thirds vote.

The Intermediate-range Nuclear Forces treaty, signed Dec. 8 by President Reagan and Soviet leader Mikhail S. Gorbachev, requires the elimination within three years of all missiles with a range of 300 to 3,400 miles.