The new chief U.S. delegate to the Law of the Sea Conference said today that the Reagan administration wants to reopen the entire text of the treaty governing use of the oceans.

Reacting with shock, representatives of the 150 other delegations to the conference, warned that the move could destroy the pact, which had been tentatively agreed on after seven years of negotiations.

James L. Malone, who was named head of the U.S. delegation Saturday after the abrupt dismissal of the previous chairman, George H. Aldrich, and other career foreign service officers, made the statement to reporters just before the opening of the 10th session of the conference here.

We're going to subject the draft treaty to an intense review," Malone said. "We've made no judgment for or against it, but the president and the new administration feel we need a thorough study."

Last Thursday, a State Department official told a Senate subcommittee that most of the draft document was satisfactory and that only one section -- dealing with deep seabed mining -- would be reopened by Washington.

Malone, asked today if the administration had changed that position, said that mining is an area of concern but that "we want to look at the entire text."

The official who testified before the Senate subcommittee was George D. Taft, director of the department's Law of the Sea Office and a veteran of the negotiations. Taft and Aldrich were among several career foreign service officers removed from the delegation.