The United States will deploy more than 500,000 military personnel in the Persian Gulf region during the war with Iraq, a number that approaches its maximum troop strength in Vietnam after more than three years of mobilization, U.S. officials predicted yesterday.

This total is at least 15 percent greater than the number of U.S. troops expected to be deployed for Operation Desert Storm by many lawmakers and publicly predicted by some military officials after President Bush's commitment of additional troops in a second phase of the buildup beginning in November.

Several congressional officials expressed surprise at the latest forecast, but they noted that with public and political attention riveted on the massive U.S. and allied air offensive against Iraqi forces, the continuing deployment of tens of thousands of U.S. ground troops and their accompanying weapons to Saudi Arabia has attracted little attention.

Since the beginning of the war on Jan. 17, roughly 55,000 additional U.S. troops have arrived in the Persian Gulf region on ships and planes from Europe and the United States, to reach a total of about 475,000 personnel, according to the Defense Department.

Virtually all of these new additions are assigned to the Army, Navy and Marines; the number of Air Force personnel has increased by only 5,000.

Military officials said these deployments provide a barometer of the readiness of various U.S. forces to take part in the war. With additional Army and Marine troops arriving daily, they said, any ground combat is unlikely to begin soon.

"We are still a considerable distance in time from the point where the Army chief of staff and Gen. {H. Norman} Schwarzkopf are going to feel comfortable with beginning a ground campaign," an Army official said in discussing the additional deployments. Schwarzkopf is commander of U.S. forces in Saudi Arabia.

Officials said the new deployments also underscore the U.S. military's expectation of the need for eventual ground warfare against surviving elements of the estimated 545,000 Iraqi troops deployed in Kuwait and southern Iraq, after the initial phase of U.S. and allied aerial bombardment. The deployments are expected to give the coalition arrayed against Iraq about 530,000 combat ground troops in Saudi Arabia alone, up from the Jan. 15 tally of 467,000 troops.

"I think there's not much doubt that we'll go over 500,000," a senior defense official said. "If you look at what's already in the {mobilization} pipeline, there's no way to avoid it."

Army Lt. Gen. Calvin Waller, deputy commander of U.S. forces in Saudi Arabia, told reporters on Dec. 19 that the final U.S. military deployment would be about 430,000 personnel.

But since then, Schwarzkopf has requested additional specialists and a few more military units to "round out" the ground forces he then had in place or en route, officials said.

Three more Navy aircraft carriers and about 15 more combat ships have reached their stations in the gulf since the outbreak of hostilities, in addition to the estimated 80 ships already present there. The carriers alone have an estimated 6,000 sailors each.

Extensive training of these new forces is still underway, U.S. officials said. "Ground forces continue to hone their combat skills and continue to conduct live fire . . . weapons training. . . , {antitank} gunnery . . . , artillery training and vehicle maintenance" exercises, Army Lt. Col. Greg Pepin said Sunday.

"Our land operations . . . continue unhampered in terms of training, unloading of stocks and planning.

And the huge logistic effort means that, coming out of the ports and airheads, one truck leaves every 15 seconds," said Maj. Gen. Alex Harley, assistant chief of the British defense staff, about the coalition's ground forces in Saudi Arabia this week.

Several officials said the U.S. deployment has swiftly crept upward without any formal new White House or Pentagon decision. "This is an outgrowth -- a fine-tuning -- of the decision we made in November. It's not as if we called a meeting to order a mid-course correction," one official said.

The United States deployed 536,000 military personnel in Vietnam at the height of the conflict in 1968, a large jump from its force of 184,000 three years earlier. In the current war, a comparable buildup will have taken place in just three months.

Most of the additional troops are in active-duty units transferred from Europe and reserve forces.

The Army, for example, announced yesterday it was calling to active duty 8,478 more reservists and National Guard members from 22 states, Puerto Rico and the District of Columbia. These reservists follow more than 190,000 such personnel called to active duty since U.S. troops were deployed to the Persian Gulf in August.

President Bush last week authorized the military to tap its Individual Ready Reserve, a pool of reservists who do not belong to organized units. Defense Secretary Richard B. Cheney also authorized the Army to call up 220,000 reservists, nearly double the previous ceiling.

The Navy, Marines and Air Force were also authorized to double their reservists to reach a total of 140,000.

The potential length of service for each reservist was also extended from 180 days to one year.