With U.S. senators, military brass and bands and the requisite television celebrity on hand, what officials described as the world's largest USO lounge opened yesterday at Baltimore-Washington International Airport.

As many as a quarter-million military personnel and family members are expected to use the lounge this year during their travels, more than any other USO facility in the world, according to officials with the nonprofit agency that supports U.S. troops. The $1.1 million, 5,000-square-foot USO International Gateway Center features an array of attractions for traveling troops, including a nursery, a TV lounge with a 72-inch screen, a sleeping room, a technology center with computers and on-line access, a baggage room, and free coffee and doughnuts.

"I only wish I was a Rockette, so I could burst into song," U.S. Sen. Barbara A. Mikulski (D-Md.) told a large crowd at yesterday's ribbon cutting.

About three-quarters of U.S. military personnel being sent to Europe or the Middle East now come through BWI, according to military officials, making the Anne Arundel County airport the biggest U.S. gateway for overseas troop deployment.

More than 154,000 people moved on military flights through BWI in 1999, according to the U.S. Air Mobility Command (AMC), which is responsible for transporting troops for all U.S. military branches.

"Millions, literally millions of soldiers, sailors, airmen and Marines are going to be transiting through this lounge in years to come," said Gen. Charles T. Robertson, commander of AMC, who attended yesterday's ceremony with the Air Force chief of staff, Gen. Michael Ryan, and actor James Brolin, star of the weekly TV series "Pensacola: Wings of Gold."

If AMC were an airline, it would be the largest carrier at BWI's struggling two-year-old, $140 million international pier. Nearly one in five international passengers traveling through BWI in 1999 flew on AMC flights, according to figures from the Maryland Aviation Administration.

"Having AMC come to BWI was a great step forward for the airport," said Sen. Paul S. Sarbanes (D-Md.), who said the military flights generate commercial business for BWI.

Most weeks, AMC operates about a dozen flights from BWI to locations including the United Kingdom, Germany, Iceland, the Azores, Italy, Spain, Turkey, Kuwait and Saudi Arabia. The flights are not on military aircraft, but on wide-bodied jets chartered by AMC from private companies.

On a recent afternoon, people moving through BWI included a detachment of Air Force security police being sent to Riyadh, Saudi Arabia, for a 90-day rotation, Army soldiers being transferred to Germany, soldiers reporting to Aberdeen Proving Ground for training, and military family members returning overseas after extended holiday breaks at home.

Troops rotating out of six-month assignments to peacekeeping missions in Bosnia or Kosovo also are moving through BWI, officials said.

"These are America's sons and daughters heading off to some places that may not be very comfortable," said Betsey Sanpere, spokeswoman for the Maryland Aviation Administration.

In the days leading up to Christmas, "the whole airport turned into a sea of green," said Adrienne Schultz, director of the USO lounge.

Troops are often traveling in civilian clothing but are generally easy to spot. "They're the ones with 52 bags," Sanpere said.

The military traffic brings Maryland about $25 million annually from visitor and other expenditures and also generates about $1.5 million in airport revenue, officials said. "They were recruited here with that in mind," said David Blackshear, executive director of the Maryland Aviation Administration.

BWI's role as a military gateway stems from a 1997 decision by AMC to replace Philadelphia International Airport as its northeast gateway beginning in February 1998. The closing of the Philadelphia Navy Yard prompted the Air Force to consider moving its operation to an area with a bigger concentration of military facilities, in particular the Washington region.

The Air Force considered Dulles International Airport, but Sarbanes and other Maryland members of Congress lobbied the Air Force to choose BWI, arguing that it was less expensive and congested than the Virginia facility.

Although AMC oversees a fleet of about 1,400 military aircraft, ranging from giant C-5 Galaxys to workhorse C-130 Hercules, military officials said it is more economical to move troops overseas on charter flights. The military cargo planes are used primarily for moving equipment and supplies and for moving troops within a theater.

Even during the Persian Gulf War, about 90 percent of the half-million U.S. troops sent to the Middle East traveled on charter aircraft, according to Lt. Col. Chuck Wynne, a spokesman for AMC.

AMC has its own counter in the international terminal, between Air Jamaica and El Al airlines, where soldiers check in for flights and pick up boarding passes. Electronic boards in the international pier show the military flights next to commercial flights to holiday spots such as Montego Bay, Jamaica. But military flights to Kuwait and Saudi Arabia are not posted for security reasons, officials said.

Not all the military travel is business-oriented. The Air Force runs a space-available system, known as Space A travel, which allows military personnel, family members and retirees to take empty seats on military flights for a nominal fee. "They can go to England, Spain or Portugal for $12," Schultz said.

As part of its effort to lure the military to BWI, Maryland paid for the construction of the lounge and provides cleaning services.

Operating the lounge, which is run by about 100 volunteers, will cost between $200,000 and $250,000 annually, according to Elaine Rogers, president of the USO of Metropolitan Washington. Most of the money comes from corporations, including Microsoft, Cendant, AT&T and Lockheed-Martin. "This is a big project for a nonprofit to take on," she said.

Blackshear said Maryland officials have no concerns that the military traffic could make BWI a target for terrorism. "None whatsoever," he said.

However, the airport had to be evacuated in November when, in separate incidents on the same day, two military personnel tried to carry inert souvenir grenades onto commercial aircraft.