By the time they gathered in the lobby of Bethesda Naval Hospital yesterday, they figured they had just about run out of tears. They were wrong.

The second half of the medical staff assigned to the USNS Comfort hospital ship embarked yesterday on an uncertain mission in the Middle East. After an emotional ceremony at Bethesda, they flew out of Andrews Air Force Base last night aboard a chartered Boeing 747 to rendezvous with their ship in Rota, Spain.

The slow-moving Comfort sailed out of Norfolk across the Atlantic on Aug. 14 with the other half on board.

The tearful farewell at the naval hospital before the 400 medical personnel shuttled to Andrews ended a tortuous week of waiting by the phone, hanging on every newscast and finding new ways of saying goodbye.

"This is normal if you're from Norfolk or San Diego, where ships leave all the time," said Lt. Cmdr. Doris Vaiana, a nurse who was left behind because she is pregnant. "But this is Washington, where we deal in red tape. You don't see this around here."

Since the Baltimore-based Comfort sailed last week, the men and women attached to its crew knew it was only a matter of time before they were ordered to fly out to join the ship. Each night, they called other crew members or a Navy hot line. Finally, the word came Monday night: Report in uniform with no more than 66 pounds of luggage, prepared for six months at sea.

"It's been a helluva week," said Joseph Walker, 20, who was crying uncontrollably at one point as he clutched his 23-year-old sister, Ensign Joann Walker. "We've had all kinds of parties. We had a going-away party every night."

"It's been real trying time, real emotional" for the Bethesda family, said his aunt, Pat Reitz. "Up and down, up and down."

With a Navy band playing martial music and with banners wishing them "Fair Winds and Following Seas," the nurses and medical technicians said goodbye to wives and husbands, children and parents, friends and co-workers.

Ensign Walker said she was glad it was finally time to go. "I've been crying for a week and a half," she said, dry-eyed as her relatives broke down around her. "I'm dehydrated."

Outside the hospital, a composed Lt. Taryn Ellison, of Reston, sat on the curb with her boyfriend, Bob Pittman.

"I've done a week's worth. I think I'm all cried out," the nurse said, laughing.

"My biggest fear is not coming back. I can live with the separation. I can't live with the idea of not coming back."

For the most part, crew members seemed far more upset at leaving family and friends than concerned about their own safety. But boyfriends, wives and parents weren't nearly so sure Saddam Hussein would respect the red cross painted on the Comfort's stern.

"I'm not worried about being hurt," said Tracy Davis, 21, a medical technician from Washington who was holding both his girlfriend and the stuffed dog she gave him when they started dating two years ago. "I'm worried about being over there for a long period of time."

Girlfriend Angela Smith, 23, of Washington, shook her head. She was worried. "Anything could happen," she said. "You don't have any guarantees."

The 894-foot, 69,360-ton Comfort is one of only two military hospital ships in the world -- the other, the California-based USNS Mercy, is also en route to the Middle East. The Comfort's 1,000 beds and 12 operating rooms make it larger than most hospitals that don't float.

As a noncombatant, the ship and its 900 medical personnel are officially protected by the Geneva Convention. The Comfort will support the four aircraft carrier battle groups and tens of thousands of infantry soldiers mobilized to defend Saudi Arabia.

The ceremony at Bethesda before the Navy men and women boarded 10 Naval Academy buses for Andrews was half festive, half somber. The mood was much like when parents leave grown children at college freshman orientation, though with a sharper edge.

Even the Navy's surgeon general, Vice Adm. James A. Zimble, seemed choked up when he told the assembled crew, "I've never been more proud."

Lt. Cmdr. Melanie Frank, of Gaithersburg, was contemplating what she will miss while she is gone -- watching her 7-year-old son, Evan, start gymnastics and go for his red belt in karate and seeing her 3 1/2-year-old daughter, Lauren, enter preschool next month.

"We won't be able to do that now," she said, choking up with tears as Lauren buried her face in her mother's shoulder.

"It's something you have to expect," said her husband, Cmdr. Joel Frank. "I'm excited she's going. I've had my sea duty, and this will be her sea duty. I know the Navy will take care of her."

Over near the buses, Lt. Denise McDowell and her husband, Ken, of Gaithersburg, joked to keep their emotions in control, while their first child, 12-month-old Caitlin, crawled around in the grass.

"I'll tell her you're at the grocery store," Ken told his wife. "For a long trip."

"Yeah, Fort Meade," she replied. "The traffic was real bad."

Denise, a 31-year-old nurse, said leaving her daughter is the hardest thing she's ever had to do. And Ken, a 41-year-old banker, said taking care of Caitlin will offer challenges he never expected.

"This is a sobering realization, quite sobering," he said. "I've had to take a crash course in single parenting -- when the immunizations are done, when to start weaning off the bottle, what kinds of food are okay."

Denise knelt on the ground and signaled Caitlin to come to her. The toddler took a few halting steps, fell to her knees and then crawled the rest of the way, gurgling all the time.

Ken watched with a forced smile. "She's going to be running by the time Mom gets back," he said.