U.S. and Saudi defense officials are discussing whether to extend joint air coverage to the southern portion of the Persian Gulf in an effort to help protect Kuwaiti oil tankers flying American flags, according to administration sources.

Extension of the air "cap" for surveillance and defense is militarily less important to Pentagon planners than gaining access to Saudi airfields on at least a temporary or contingency basis to support U.S. warplanes that may be needed to defend "reflagged" Kuwait ships.

But a Saudi decision to join the United States in helping defend gulf shipping outside the kingdom's territorial waters would signify a major shift in Saudi policy. Thus far, the Saudis have refused to become more involved for fear of being too visibly associated militarily with the United States in a way that could invite Iranian retaliation.

One Pentagon official said it appears "possible" that the Saudis might agree to extend the cap to the lower gulf.

"Expanded AWACS {Airborne Warning and Control System} coverage that doesn't involve increased U.S. presence in Saudi Arabia is probably manageable for the Saudis," said James A. Placke, a former State Department official who is now a Middle East consultant. Placke added that the Saudis had told Washington "for years and years" they would be willing to do more to help the United States militarily, "if we could do it confidentially."

The defensive cap over Saudi land and gulf waters is now provided on a 24-hour basis by four U.S.-manned AWACS aircraft based since 1980 in Saudi Arabia for which Saudi-piloted F15 fighters provide protection. The Saudis also have taken possession of five additional AWACS of their own, making a total of nine such aircraft now stationed in the kingdom.

Extending the cap would involve either the U.S.- or Saudi-owned AWACS flying into the southern gulf waters protected by Saudi F15s or American fighters from an aircraft carrier outside the gulf, according to U.S. officials.

The U.S. quest for additional Saudi military assistance has set the stage for another difficult test of the U.S.-Saudi relationship. It comes in the wake of the Iraqi attack on the USS Stark and allegations in Congress that the Saudis failed the United States by refusing to intercept the Iraqi warplane involved in the incident.

From the U.S. side, the test involves Saudi willingness to help the United States provide protection to the reflagged Kuwaiti ships as part of its defense of international shipping in the gulf. For the Saudis, the stakes again involve U.S. reliability as a defense partner and willingness to continue selling weapons to the kingdom.

The administration recently notifed Congress it intends to sell the Saudis 1,600 of the latest version of the air-to-ground Maverick missile for $360 million. The proposed arms sale has touched off opposition in the Senate and House, with 52 senators and more than 100 House members already supporting a resolution to block the sale.

U.S. officials suggest that a Saudi agreement to extend AWACS air coverage into the lower gulf could also ease congressional opposition to the Maverick sale, as well as an additional squadron of F15s and upgraded equipment for U.S.-made tanks the Saudis want to buy.

For the United States and Saudi Arabia, the issue of mutual reliability has become major once again.

"Confidence is not a ready commodity right now," said Mazher Hameed, a Saudi military analyst and director of the Washington-based Middle East Assessments Group. "Saudi Arabia would like the United States to become a factor for maintenance of the status quo in the gulf, but the problem is, can you rely on the United States?" Hameed predicted that the Saudis will make "some concessions" to the U.S. requests for greater Saudi military cooperation. But he added, "I think they are also going to make some demands of Washington for new arms in return."