The chief Philippine negotiator in talks on U.S. military bases said Thursday the Philippines may defer a constitutional provision banning nuclear weapons at the facilities.

Foreign Secretary Raul Manglapus also said Philippine and U.S. delegations have made progress on major issues since the talks resumed last week following a walkout by the Philippine side July 26 in a dispute over monetary compensation.But Manglapus said he did not foresee an early conclusion of the talks, which began April 5 to review the terms of the 41-year-old treaty covering Clark Air Base and Subic Bay Naval Base, the largest U.S. military installations outside the continental United States. Officials had originally hoped to finish with the review last month.

President Corazon Aquino has said she is keeping her options open on a renewal on the pact that expires in 1991.

Asked about discussions on the nuclear-free provisions in the newly ratified constitution, Manglapus said the Philippine delegation was following guidelines issued last month by Sedfrey Ordonez, Aquino's justice secretary and chief legal counsel.

The Constitution says, "The Philippines, consistent with the national interest, adopts and pursues a policy of freedom from nuclear weapons in its territory."

In a ruling interpreting the provision, Ordonez said the national interest provision permits Aquino to "defer" implementation of the nuclear ban and that the president may "negotiate a modification or extension" of the bases pact.