RIYADH, SAUDI ARABIA, AUG. 25 -- Seventeen days after President Bush ordered a massive deployment of U.S. forces, military leaders say they are just beginning to disperse their most formidable ground troops to strategic military and industrial sites across this desert kingdom.

As the buildup of heavy tanks, armor, attack planes and helicopters takes shape on the desert floor, military leaders are preparing for a protracted operation. Several months from now, the U.S. forces could be large enough to launch an attack against Iraqi troops if Bush ordered one, some officials said.

Within a month, Marine Corps officials expect to have up to half of all their combat troops and aircraft in Saudi Arabia and surrounding nations -- up to 50,000 fighting forces and possibly tens of thousands of support personnel.

The Army's most heavily armed fighting forces have begun arriving in only the last few days, with the first sand-colored M-1 Abrams tanks of the 25th Mechanized Division rolling off ships from the United States this weekend.

Plans call for Saudi military forces to be assigned to the area along the Kuwaiti border, with U.S. ground troops protecting key strategic locations, according to interviews with numerous U.S. military officials throughout Saudi Arabia.

Marines and elements of the 24th Mechanized Division, with its heavy tanks and armor, will be positioned around a key port and oil refinery region. The AV-8B Harrier "jump jet" will provide close air support, and the F/A-18 Hornet fighter could be used for air strikes. More Marines may be deployed aboard amphibious assault ships in the Persian Gulf, off the coasts of Kuwait and Saudi Arabia.

Large numbers of Army units, backed by Apache attack helicopers, have been ordered to protect key Saudi oil fields. Patriot missile batteries have been erected at several strategic locations to intercept Iraq's Soviet-made Scud missiles and its attack planes. Air Force F-15 Eagle fighter jets have been patrolling the border skies around the clock with their Saudi counterparts. In addition, special forces commandos, including Navy Seals, have been given missions throughout the area.

Other powerful weapons that could be used to strike Iraqi targets include F-117 "stealth" fighters and A-10 attack planes. And steaming offshore will be the potent force of the battleship USS Wisconsin with its nine 16-inch guns. But the most massive influx of foreign troops in Saudi Arabian history has raised some problems for U.S. military commanders here. The Saudis, for example, have not yet allowed American forces to conduct training exercises with live ammunition, which they need to prepare for battle.

"Until you've experienced this buildup, it's hard to contemplate it," said Lt. Gen. Walter E. Boomer, commander of Marine Corps forces here. "It's an overwhelming kind of thing. Any country into which this amount of equipment and this number of people has been moved would have problems dealing with it."

The largest mobilization of U.S. troops in the last 50 years also has raised serious questions about the long-term mission of the U.S. military in this oil-rich country.

"How much is enough?" said Lt. Gen. Charles A. Horner, who has headed the U.S. Central Command's operation here. "That's a tough question for a military man to answer. . . . If he errs, he probably errs to the far side."

Boomer, who on a 115-degree summer day said he has already ordered winter field jackets for his troops in preparation for the desert's cold winter nights, described his mission here with the same unspoken allowances for potential change as many ground commanders. "Our mission is defensive. Right now it's the only mission I have," he said.

But Iraqi President Saddam Hussein's strategy of moving U.S. and other Western hostages to key military and industrial installations adds a dangerous element to any potential U.S. military action. "It makes the equation more difficult and the president's decision more difficult," said Boomer.

Although the military moved hundreds of fighter planes and Patriot air defense missiles into Saudi Arabia during the first days of the operation, the initial wave of ground combat forces has only begun arriving in the past several days. Military leaders and troops assigned here said the first days of the operation were extraordinarily tense because of the small number of U.S. forces and weapons in Saudi Arabia. "We feel more comfortable every night when we go to bed," said Horner.

Most of the heavy combat forces have not yet arrived in Saudi Arabia, and most of those that have reached the area have been busy organizing their units and acclimating troops to the scorching desert heat. Only in recent days have ground troops begun short training exercises.

The full contingent of combat forces is not expected to arrive in Saudi Arabia for another six to eight weeks, according to military officials.