Surgeons at Children's Hospital in the District yesterday successfully separated 4-month-old girls conjoined at the chest and abdomen in an emotional day-long operation that their grateful parents described as "the best Father's Day gift ever."

Cheers and applause broke out in the crowded operating room as lead surgeon Gary Hartman snipped through the last centimeter of tissue connecting Jade and Erin Buckles, whose rare condition had rallied an elite medical team of two dozen specialists.

Grinning broadly, the hospital's chief of surgery, Kurt Newman, emerged just 21/2 hours after the first incision was made.

"You've now got two babies that are separate, and they're both doing well," Newman told Kevin and Melissa Buckles, who spent the day anxiously waiting in a hospital playroom, isolated from other patients and families.

Melissa Buckles, a 30-year-old high school teacher, buried her head and cried on the shoulder of her husband, a 34-year-old Marine whose bloodshot eyes reflected the sleepless night the Woodbridge couple spent in the hospital after the twins were admitted Friday.

"I thank you so much," Melissa Buckles told Newman. "We've always considered them two little girls, but . . . "

Newman described the mood in the operating room as "absolute elation" when the girls were separated.

"This is probably the best Father's Day gift ever," Melissa said, echoing a hope Kevin voiced days earlier.

The babies were reported to be in critical condition in separate isolettes in an intensive care unit, where their recovery was expected to last a few weeks to a few months, depending on complications. The hospital has estimated the cost of their care at upward of $1.5 million. Prepping, surgical separation, closing the wounds and stabilizing the girls took about eight hours -- nearly half as long as the parents had been told could be the case.

"We know they're still not necessarily out of the woods," said Kevin Buckles, an assistant drum major in the Marine Drum and Bugle Corps who made a friend promise before the surgery that he would play taps for the girls if they died on the operating table.

The 22-inch-long babies were each left with a 61/2-inch wound from sternum to bellybutton, leaving them vulnerable to dangerous infection.

Erin was first out of the operating room. In the intensive care unit, her parents leaned over her bandaged body. "Hi, sweetheart," Melissa said, stroking the baby's thigh. "We love you."

Conjoined twins are considered the rarest of human births, with only 700 sets born alive in recorded history. Jade and Erin were delivered by Caesarean section Feb. 26 at National Naval Medical Center in Bethesda by Christian Macedonia, who came to Children's yesterday to watch the separation on a live video feed from the operating room. "Amazing, just amazing," Macedonia murmured as a surgeon's gloved finger peeled back a protective sac to reveal two small hearts nestled tongue-and-groove, beating in synchronicity.

Surgeons encountered fewer complications than anticipated, Newman said. The girls' large, shared liver was easily divided, and the hearts turned out to share only a small bridge of tissue. As diagnostic tests had revealed, the tip of Erin's heart protruded into Jade's chest. The organ proved more maneuverable than expected, however, and was tucked back into Erin's chest.

The twins were expected to need reconstructive surgery as they mature.

Their father said before the operation that he would prefer not to ever tell Jade and Erin that they were conjoined, but that "I know when they get older, they'll have questions like, 'Where did this huge, mother scar come from?' The most important thing we want them to know about it is that being conjoined is not what made them special to us."

The Buckleses have a 2-year-old daughter, Taylor, and Kevin Buckles shares custody of son Kevin Jr., 11, who asked to stay home during the operation and be briefed by telephone. The pigtailed Taylor, wearing a pink "Big Sister" T-shirt, spent the day at the hospital, distracting her mother with games of hide-and-seek in the waiting room. Kevin Buckles tried to take his mind off the agonizing wait by studying books on combat techniques for an upcoming promotion exam.

While the Powerpuff Girls fought endless cartoon evil on a wall-mounted TV in the playroom, hospital staffers one floor above gathered around a wide-screen monitor to watch the live video from the operating room, where surgeons wore tiny cameras attached to their caps. An audio feed broadcast the team's voices as the surgeons asked for knives and retractors.

"Not that I don't trust you," Hartman could be heard to say, addressing a vein as he cut smoothly down an incision line drawn in purple marker across the fleshy bridge where the twins were fused.

At the hospital, the emotional day began shortly before 8 a.m., when the weeping mother walked the twins to the operating room, where anesthesiologist Ramesh Patel was waiting.

"Mom?" he prodded, reaching for his tiny patients.

Both parents took turns kissing the girls goodbye, then watched them disappear behind the swinging doors. Mother and father headed back down the hallway, Kevin holding his daughters' favorite plush yellow duckling and Melissa clutching empty white blankets embroidered in pink satin: Jade Hope and Erin Faith.

Hartman, on his way to scrub in, stopped when he saw the couple.

"You okay?" he gently asked Melissa. "We'll take good care of them."

The plastic surgeon, Michael Boyajian, was around another corner.

"Take care of my girls," Melissa implored him.

"Handing off the girls was probably the most difficult thing I ever had to do," Melissa said later. "It's hard to prepare for something like this."

The past week had tumbled past in a blur of minor catastrophes for the family. Melissa's mother arrived from Minnesota to help out, only to fall down the stairs and fracture her ankle, forcing her to return home. The downstairs toilet broke, and on the day before the surgery, power went out in the Buckleses' townhouse for four hours. Kevin then tripped over the family cat, Ninja, and fell down the stairs himself. "I almost lost a cat," Melissa said.

Although psychologists have assured the parents that the girls are too young to experience a deep emotional response to the sudden loss of a sister whose face was always mere inches away, they said the babies will miss the physical sensation of being connected. As the twins' conditions improve and the girls are less sedated, doctors might decide to place miniature sandbags next to the girls to simulate the missing weight.

Experts also told the parents that the babies would recognize and respond to familiar scents and sounds. Before surgery, Melissa misted a baby blanket with her perfumed body spray. The parents also tape-recorded the girls cooing and gurgling to each other, hoping that the sound of the sister suddenly gone would provide comfort in the long weeks ahead.

Staff writer David Brown contributed to this report.

Jade Buckles is moved from the operating table that held her and her twin sister, Erin, rear, during their surgery at Children's Hospital.Melissa Buckles' eyes well up as she, with husband Kevin, hands the twins to Ramesh Patel.A team of doctors and nurses, foreground, checks monitors as the surgery progresses behind them at Children's Hospital.Melissa and Kevin Buckles visit daughter Erin after she was surgically separated from her sister.