MANAMA, BAHRAIN, AUG. 19 -- U.S. warships in the Persian Gulf region delayed taking action today against two Iraqi tankers that defied U.S. warning shots Saturday and refused to halt, while Defense Secretary Richard B. Cheney said he would not "speculate on what happens next."

The tankers, believed to be filled with oil, continued on their outward course from the gulf toward the Arabian Sea and appeared to pose the first real test of America's willingness to enforce its stated intention of stopping and searching vessels suspected of being involved in Iraqi trade banned by United Nations sanctions.

White House Press Secretary Marlin Fitzwater told reporters aboard Air Force One: "We intend to enforce the sanctions, but we want to give them every opportunity to turn around and change course." He would not say whether the United States would use force against the tankers but added, "Our only concern is that they not offload and violate the sanctions."

In the Red Sea, meanwhile, interception of a Sudanese vessel by a U.S. warship prompted diplomatic protests by Sudan and Jordan, which charged that the vessel turned away was en route to Aqaba, Jordan, to pick up hundreds of Sudanese refugees who had fled Iraq and Kuwait. U.S. officials said the ship appeared to be carrying cargo that violated U.N. sanctions against Iraq.

Cheney said the Iraqi oil tankers, the first ships to refuse to halt when challenged by U.S. warships, are "still under surveillance and they are not close to any port or any harbor at this point." One reportedly was at the south end of the Persian Gulf and the other beyond it, in the Gulf of Oman. Their destinations were not known, U.S. officials said.

Administration officials have indicated that the United States is awaiting a U.N. vote to reinforce support for military force in maintaining a worldwide trade boycott against Iraq and is hoping to gain assistance of other nations' warships in any confrontation with the Iraqi vessels.

Iraq has warned that if further attempts are made to halt the vessels, there will be "grave consequences." Iraqi Foreign Minister Tariq Aziz today called the U.S. efforts to halt shipping "piracy and armed aggression," and he demanded that the international community condemn them, Iraq's official news agency reported.

While U.S. officials say they believe U.N. resolutions have authorized navy warships to interdict vessels that ignore the embargo, some administration authorities say they would prefer a reinforcing resolution strictly addressing military action.

"We obviously are prepared to see to it the sanctions the U.N. voted and the legitimate government of Kuwait asked us to undertake are carried out," Cheney told reporters today during a three-hour visit to a key staging base for U.S. troops and equipment arriving in Saudi Arabia.

"Our forces are authorized to intercept shipping that they have reason to believe may in fact be violating the sanctions," he said, adding: "We want to continue to work both by voluntary means and by naval means, if necessary, to see to it that the sanctions are enforced."

As U.S. forces and arms continued to pour into the region, Cheney, speaking on ABC-TV's "This Week With David Brinkley," said that the intention was to "put enough forces in Saudi Arabia to deter" a military conflict, and that "should {Iraqi President} Saddam Hussein be foolish enough to launch an attack on Saudi Arabia, {U.S. forces} would be able to do a very effective job of making him pay us a bit of a price for that."

Sources said, however, that the United States would feel much more comfortable when it has more troops in Saudi Arabia.

In one of the confrontations with the Iraqi tankers, the frigate USS Reid fired six shots across the bow of the Khanaqin on Saturday as it moved south through the Gulf of Oman after refusing to heed radio calls from U.S. ships. Meanwhile, the frigate USS Bradley and the guided-missile cruiser USS England fired three shots in front of the Baba Karkar, which was steaming south in the Persian Gulf after it failed to respond to radio warnings.

In another incident Saturday, a search team from the USS England conducted the first on-board inspection of a vessel by a U.S. warship as a result of Bush's interdiction order Thursday.

Officers aboard the England asked the Chinese ship Heng Chun Hai for permission to board after U.S. authorities became suspicious about its cargo, according to Pentagon officials. The boarding party discovered fertilizer from Iraq on the southbound ship and ordered it to return to its port of origin. Pentagon officials said it is now at anchor in the Persian Gulf.

Reports conflicted on the interception that led to diplomatic protests by Sudan and Jordan. According to U.S. officials, the destroyer USS Scott intercepted the Dongola, a Cypriot cargo ferry flying the flag of Sudan, which was believed to be loaded with aluminum chromate, a chemical used in the manufacture of some chemical weapons. The ship was headed toward the Jordanian port of Aqaba, but turned away just outside the Red Sea Gulf of Aqaba after the Scott's warning.

The governments of Sudan and Jordan both complained that the vessel was en route to Aqaba to pick up 800 Sudanese refugees who had fled Iraq and Kuwait since the Iraqi invasion of Kuwait Aug. 2.

The foreign ministries of both Jordan and Sudan called in the U.S. ambassadors to protest the action, Washington Post correspondent Nora Boustany reported from Amman, Jordan.

Jordanian Foreign Minister Marwan Qassem called the incident "obstructive" to Jordan's efforts to deal with the "human problem" of tens of thousands of refugees reaching that country from the war zone.

In Khartoum, Sudanese Foreign Minister Ali Sahloul described the U.S. action as a "dangerous precedent" because the vessel involved was not Iraqi.

The Sudanese News Agency said U.S. diplomats told Sahloul that "American authorities had no objection to the ship's continuing its voyage on condition it submitted first to inspection and then carried the Sudanese and their luggage only."

Cheney continued his four-day trip to the region with consultations with the leaders of Bahrain and a visit with U.S. troops and pilots at a base in Saudi Arabia. He is scheduled next to visit Oman, the United Arab Emirates and Egypt to solicit continued support for the international efforts against Iraq.

Several of the Arab leaders are expected to ask Cheney for more arms as a result of the Iraqi invasion and their participation in the multinational efforts to oppose it.