WITH U.S. FORCES, SAUDI ARABIA, DEC. 17 -- Large numbers of troops have begun arriving in Saudi Arabia in a buildup designed to raise the strength of U.S. forces in the Persian Gulf to 430,000 men and women, but the deployment is not likely to be completed in time for U.S. forces to be ready for an offensive against Iraq by Jan. 15, according to senior U.S. military officials.

Members of the 2nd Marine Division have been arriving at the rate of 1,000 a day over the past week and will continue at that pace for the next couple of weeks, Pentagon officials in Washington said. When second-stage deployment finishes, the Marine presence here is expected to be approximately 90,000 men and women.

The commander of Marine forces in Saudi Arabia, Lt. Gen. Walter Boomer, told a visiting congressional delegation last week that "by Jan. 15, two-thirds of {all Marine combat forces} will be in this area."

But the Army's VII Corps, expected to add about 100,000 soldiers to Operation Desert Shield, has only begun to trickle in from Germany and the United States. Some military sources say bad weather in Europe has hamstrung flight schedules, causing delays throughout the logistical pipeline, but senior VII Corps officers insist that their timetable remains undisturbed.

"The deployment is pretty much on schedule," said Brig. Gen. Robert McFarlin, the VII Corps logistics chief. "It's not easy, but we're keeping to it. A lot of people are pitching in."

In testimony before the House Armed Service Committee Friday, Gen. Colin L. Powell, chairman of the Joint Chiefs of Staff, indicated it could be as late as mid-February before U.S. forces in the region would have full capability to launch an offensive against Iraqi forces.

"Our offensive capability is not where we would want it to be yet," Powell said.

President Bush ordered the second-stage buildup on Nov. 8. It is designed to raise the number of U.S. soldiers in the Persian Gulf from approximately 260,000 to 430,000 and to give U.S. forces the ability to mount an offensive war against entrenched Iraqi positions in occupied Kuwait and Iraq itself.

Mid-January emerged as a "deadline" only on Nov. 29, when the U.N. Security Council authorized military action if Iraq failed to withdraw its soldiers from Kuwait by Jan. 15. Defense Secretary Richard B. Cheney told the Armed Services Committee last week that Iraq has more than 500,000 soldiers deployed in Kuwait and southern Iraq. U.S. and allied forces total approximately 480,000 men and women.

The issue of whether the United States will have completed its second-stage deployment by Jan. 15 and thus be able to fight an offensive war against Iraq remains unclear -- as indicated by Powell's congressional testimony. Army Maj. Gen. William G. "Gus" Pagonis, Desert Shield's chief of logistics, repeatedly ducked the question in a recent interview, saying only that "I have a timetable, and we will do everything in our power to meet it."

And Army Gen. H. Norman Schwarzkopf, commander of U.S. forces in the Persian Gulf, also declined to name a date but told the Reuters news agency that "it would be foolish if I even tried to say to you that I wasn't focusing on Jan. 15 as a very, very important date when I darn sure want to be ready."

The Air Force, which now has about 650 combat planes in the region, is expected to add about 300 more to its force, including additional F-117A "stealth" bombers. The Navy is doubling the number of aircraft carriers in the region to six carrier battle groups, with more than 400 fighters and bombers, and is adding a second battleship, the USS Missouri, to its fleet.

Of the new carriers, only the USS Ranger, based in San Diego, has left port, Navy spokesmen said here. The Navy currently has three carrier battle groups in the Red Sea, the Gulf of Oman and the eastern Mediterranean Sea. The battleship USS Wisconsin and an amphibious assault group carrying a Marine brigade are in the Persian Gulf.

Of the four services, only the Marines have said categorically that they intend to be in place and ready for battle by Jan. 15. Four ships loaded with enough equipment to outfit an entire 16,000-member brigade for 30 days arrived in eastern Saudi Arabia Dec. 13 and began disgorging M-60 tanks, artillery, troop-carrying vehicles and containers filled with everything from toilet paper to bandages.

"Our objective is to meet this Jan. 15 time frame," said Col. Gary Dockendorff, chief of the Marine advance party charged with unloading the ships. "Figure seven to eight days to put everything together, another two to three days to see that everything works. In 10 days, we want to be able to say, 'I can fight with it.' "

The Marines who began arriving last week are forming the 2nd Marine Division, most of whose components are based in Camp Lejeune, N.C. Ever since Desert Shield began in August, the Marines have enjoyed an advantage in quick deployment because of the brigade-sized sets of equipment that have been "pre-positioned" aboard ships, which remain at sea awaiting deployment.

The ships that arrived Dec. 13 were underway off the Atlantic Coast when the second-stage buildup was announced. The equipment was first loaded in 1984 and has been periodically unpacked, examined and tested to ensure that everything is in good repair. Maintenance personnel regularly changed gaskets, turned turbine drive-shafts and replaced outdated medicines.

"Obviously, we don't need the cold weather clothing, the heaters and the hand warmers," Dockendorff said. "We've also found some administrative forms that are outdated, but we anticipated that."

For the Army, however, moving has proved more complex. Lacking ready-to-use, spare sets of gear, the deployment of VII Corps has become part of the vast supply train moving from the United States and Europe to the Persian Gulf.

Pagonis, who runs the Saudi end of this colossus with a 25,000-member logistics command, is handling at least four different types of cargo at present: food and equipment for the soldiers already in the region; special seasonal loads, such as the Christmas mail that is pouring in at the rate of 500,000 to 600,000 pounds per day; equipment for the new arrivals; and the new arrivals themselves.

Advance parties from VII Corps have been in Saudi Arabia for the past two weeks, and some VII Corps armored-division troops have even claimed their tanks. But the inflow of soldiers from Europe has been slow up to now.

Nevertheless, said Col. Ed Simpson, VII Corps deputy chief of staff, "We're on or ahead of schedule, and we are about to reach the take-off point. Very soon it's going to be coming fast and furious around here."

On Saturday, members of the VII Corps unfurled their colors in a private ceremony, not wanting to draw attention to themselves as the new kids on the block. The unfurling officially moved the corps from Germany where it served as the armored spearhead of NATO forces facing off against the Soviet bloc on the plains of Central Europe.

Besides the 1st and 3rd Armored Divisions, its two basic units, VII Corps in Saudi Arabia will add the 1st Mechanized Infantry Division, based in Ft. Riley, Kan. With three full tank divisions, VII Corps is a classic armored corps and differs significantly from the XVIII Airborne Corps, the operational command that incorporates all the Army fighting units currently in the Persian Gulf region.

The XVIII Corps includes two tank divisions and two airborne light infantry divisions, the shock troops who arrived in Saudi Arabia in August to deter Iraq from mounting an immediate invasion of Saudi Arabia. The presence of VII Corps demonstrates U.S. willingness to match armor with the Iraqis, underscoring the deepening offensive orientation of U.S. forces here.

Moving from the cool forests of Europe to the Arabian Desert terrain, said VII Corps' Simpson, will present no significant difficulties, since "the basic skills are there," but it will necessitate some adjustments.

"Germany's a little place. There you look at a map sheet and you'll see, roads, rivers, it's easy to get around," Simpson said. "This is an enormous area. Here you look at a map sheet, and you'll see brown. Anything we need in the desert we better take with us."