Defense Secretary Richard B. Cheney said yesterday he is preparing to ask President Bush for authorization to extend the tours of reservists now in the Middle East and activate more civilian troops, a statement that some officials said was timed to bolster the administration's political brinkmanship with Iraqi leaders.

Cheney said he is seeking presidential approval to keep tens of thousands of National Guard and reserve members now deployed in Saudi Arabia on active duty beyond the current six-month limit by using a law that also gives the Pentagon the authority to mobilize up to one million reserve troops.

"We have no intention of calling up one million reservists," Cheney said in response to questions at a White House news briefing. "But that's the provision that's available for me to be able to extend those people in critical skills whose services are now being utilized."

In another move heightening military readiness, Bush yesterday issued an executive order empowering the government in the event of war to demand priority over civilian needs in acquiring supplies for the military, including food, gasoline, nuclear fuel, jet fuel and transportation services. Based on a provision of the Selective Service Act, the order gives Cheney and other government officials during war the power to "place orders and require . . . prompt delivery" of any goods and services required to support the military action.

Military officials said yesterday that if Bush orders military action against Iraqi forces, the Pentagon would need authorization to activate more reserve troops. The Defense Department has called to active duty about 150,000 National Guard and reserve troops under a presidential order signed in August allowing Cheney to mobilize a maximum of 200,000 reservists. The department expects to have about 430,000 active-duty and reserve troops deployed in the Middle East by early February.

Military officials said they do not have enough reservists in many key skills -- including those in water purification, medical and certain logistics units -- to replace those units already in the region when their six-month limit begins to expire in late February. The presidential order being sought by Cheney would allow the military to keep reservists on active duty for up to two years.

Some military authorities, noting that Pentagon officials have known for several months that they would need the authority to extend the tours of reservists, suggested that the timing of Cheney's statement yesterday on the heels of the Geneva meeting was designed to augment Bush's toughening stance against Iraqi President Saddam Hussein. News of Cheney's plans to seek the additional authority was leaked to Pentagon reporters yesterday as the results of the meeting between Secretary of State James A. Baker III and Iraqi Foreign Minister Tariq Aziz became known.

"The entire process involving the activation of the reserves is designed to escalate the degrees of brinkmanship, one on top of the other," said one Pentagon official. "Mobilization increases the number of chits on the table."

Last August, Bush authorized the first phase of a three-step legal procedure activating National Guard and reserve forces. Under that provision, the military could order up to 200,000 reserve troops to active duty for a maximum of 180 days.

The Pentagon later received congressional approval to extend to one year the ceiling on reserve combat units, which require more time to train and prepare for service in the Middle East.

The presidential authority Cheney is now seeking represents the next phase -- mobilization of up to one million troops for up to two years. The third and final part of the law, which requires congressional rather than presidential authorization, would allow the military to activate its entire reserve force of 1.6 million troops.

The mobilization of the guard and reserves has been one of the most politically charged aspects of the U.S. military buildup in the Middle East. It has brought the prospects of war home to hundreds of communities across the United States as civilian police officers, doctors, factory workers and many others have been uprooted from their normal lives and dispatched to the Arabian Peninsula.

In recent years, the military -- especially the Army and Air Force -- have come to rely more heavily on reserve units, assigning them an increasing number of military responsibilities. Yet the number of reservists in many critical logistics specialities remains relatively small. Consequently, when the six-month limit expires on the activation of some units, the military will have no other similarly specialized units to replace them, according to Pentagon officials.

Both the extension of tours for reservists and the presidential order announced yesterday for emergency military provisions involve seldom-used sections of federal law.

Bush lost the authority to order civilian suppliers to set aside part of their output for defense purposes last year when the Korean War-era Defense Production Act expired. He based his action yesterday on a part of the Selective Service Act, which also covers the drafting of military troops.

One of the suppliers who could be affected by yesterday's presidential order, Chevron Corp. Chairman Kenneth T. Derr, said yesterday that while fuel companies such as Chevron would in the event of war quickly adjust refinery operations to produce more supplies, supply lines would be strained because of limited military transports for getting fuel to the gulf quickly.

Derr, whose company is the nation's largest refiner of jet fuel, said the Defense Department has been stockpiling fuel in Saudi Arabia and had not asked Chevron to increase its output. In a luncheon interview with Washington Post editors and reporters, he said it would take "about two hours" to adjust refinery operations to produce more jet fuel, but transporting it to the Persian Gulf by tanker could take weeks.

Staff writer Thomas W. Lippman contributed to this report.