DUBAI, UNITED ARAB EMIRATES, OCT. 3 -- Iran launched about 60 armed speedboats apparently at a Saudi Arabian offshore oilfield before dawn today, and Saudi Arabia sent jets and warships to intercept them and turn them back, according to sources in the Persian Gulf region and in Washington.

Saudi Arabia sent American-made F15 and F4 jets and at least two naval frigates to warn off the formation, which got within 20 miles of an offshore oil terminal at Khafji, near the Saudi border with Kuwait, the sources said. There was no indication that gunfire was exchanged. A source in Washington familiar with U.S. military reports of the incident said the Saudis conducted a "full {military} mobilization, including land troops," and sent an urgent warning to Tehran that it was ready to "make a stand" against any attack on the oilfield.

U.S. ships escorting Kuwaiti tankers south through the gulf broke away from the convoy last night and steamed toward the area of the confrontation, according to press pool reports released by the Pentagon. They halted north of Bahrain and maintained a high state of readiness, the reports said.

Tehran gave no information on the incident, and the official media of Saudi Arabia and Kuwait denied that it took place. Iran's deployment was its largest in a hostile maneuver against any Arab state across the gulf.

For the Iranians, the incident "was a test of whether the Saudis would stand or back off," a source in Washington asserted. While Saudi Arabia confronted the Iranian deployment, its denial of the maneuver underlined the great sensitivity among the Arab states of the region about any confrontation with Iran.

Most of the Iranian flotilla had retreated to the Iranian side of the gulf by dawn, but some Iranian vessels were believed to have stayed behind and were under surveillance by Saudi and U.S. warships.

Pentagon sources in Washington said U.S. intelligence sources had detected the massing of the Iranian gunboats earlier in the week near Kharg Island, where Iran operates a large oil-export facility, and that the force had begun moving across the waterway by yesterday. The sources said that, based on intelligence reports from the region, U.S. and Saudi officials believed the assault force intended to attack at least two platforms in the Khafji field. The earnings from the field's output of 300,000 barrels of oil per day are donated by Saudi Arabia and Kuwait to Iraq, which is fighting Iran in the seven-year-old gulf war.

Sources in Washington and the gulf said U.S. Airborne Warning and Control Systems (AWACS) surveillance planes tracked the Iranian boats as they zig-zagged across the gulf and sped toward the Khafji field. Shipping sources said some workers on offshore oil platforms in the area reported seeing about a half-dozen unidentified warplanes diving in the direction of the Iranian boats, but they reported no signs of gunfire.

"The Iranians pulled back and disappeared into the night," said one western official in the gulf.

A source in Washington said the Saudi Arabian government sent an emergency message to Tehran as the flotilla was crossing the gulf last night. According to this source, the Saudi government was convinced the flotilla intended to attack onshore and offshore oil installations operated by Saudi Arabia and Kuwait for the benefit of Iraq. The source said the message made clear that Saudi military forces were "going to make a stand" to repel any attack.

The USS LaSalle, command ship for the 11-ship Middle East Task Force, the helicopter carrier Guadalcanal and the frigates Thach and Ford -- which had been escorting a reflagged Kuwaiti tanker south through the waterway -- turned around suddenly last night and raced north to the area, according to U.S. officials in the region.

At the same time, a U.S. warship in the southern gulf had a tense encounter with an Iranian warship near the Strait of Hormuz. Shortly after 6 p.m. (10 a.m. EDT), a U.S. warship was heard in marine radio broadcasts warning the Iranian vessel to turn off its fire-control radar as the two ships approached each other.

"Iranian warship, this is a U.S. Navy warship bearing 291 {degrees} at 15,600 yards from you. You have locked your fire-control radar on a U.S. warship. Secure it immediately. This is your only warning."

The broadcast, monitored here, was repeated by the unidentified U.S. vessel four times in two-minute intervals. Pentagon sources said the Iranian ship left the area.

The "locking on" of fire-control radar, which is used to guide weapons to their targets, has been defined by U.S. officials as an act of "hostile intent" that could result in American warships opening fire on Iranian warplanes or naval vessels. Pentagon sources said there have been several incidents since May in which Iranian ships have scanned U.S. Navy vessels with fire-control radar.

The aborted Iranian maneuver in the northern gulf comes two weeks after U.S. special forces teams operating off warships in the waterway fired on and disabled an Iranian mine-laying vessel, the Iran Ajr. Five Iranian crewmen were killed and 26 others detained for a week before they were returned to Iran's custody at an airfield in Oman.

Iran has vowed to avenge the attack and has issued frequent threats against U.S. forces and Arab states supporting Iraq.

Washington Post staff writers Molly Moore and David B. Ottaway contributed to this report in Washington.