Rescue workers pulled a living infant from the debris of a collapsed hospital today and foraged through the rubble for several other survivors pinned alive under the concrete since an earthquake struck Mexico City a week ago.

At least three other babies have been found in the wreckage of hospitals in the past two days.

Mexican, American and French rescue specialists at Juarez Hospital handed the days-old baby boy to doctors at dusk after a day of painstaking progress through the twisted ruins. A medical crew working under a tent immediately inserted intravenous tubes and put the infant into an incubator, while the rescue workers returned into their passageway in search of two more infants and a woman who they said were still alive in the heap of rubble that had been Juarez Hospital.

The infant's condition was not immediately known.

The extraordinary survival of the infants who had been buried under the rubble for days is perhaps the most dramatic aspect of the rescue operation with television images of the rescues gripping audiences here and around the world.

The rescue workers' efforts, scraping through debris with pickaxes and passing it out of their passageway in a straw basket, appeared to represent the last hope of finding any more than isolated survivors in the more than 300 buildings destroyed when the earthquake hit.

An 8-day-old girl and a 33-year-old man were pulled from the wreckage of the General Hospital early this morning after miraculously surviving almost a week under the rubble. The baby, who reportedly was sheltered by a dead body, was reported in fair condition, but the man suffered only a broken foot, a doctor said. Since then rescue efforts were ended at that hospital.

Early yesterday morning, a newborn boy and a 20-month-old girl were taken alive from their cribs under the wreckage of Juarez Hospital after rescue workers had dug for hours, listening to the babies' cries. The metal rails of the cribs apparently protected the children from being suffocated by the wreckage.

"When I began to go through all the rubble, I was desperate to save them quickly and the tears fell," Miguel Gonzalez Juarez told The Associated Press.

U.S. Ambassador John Gavin identified a sixth American victim of the quake as Bruce Sloan of New Market, N.H., United Press International reported. Gavin also said at a news conference that 28 Americans are still missing and most are "believed to have been in hotels that collapsed."

Mexican authorities have begun demolishing most of the other buildings where large numbers of people were trapped by the tremor at 7:19 a.m. last Thursday, in some cases spraying with disinfectant to prevent spread of disease from decaying bodies. Experts here said anybody pinned under the rubble was unlikely to survive more than seven days. But rescue workers, at first using ultrasensitive listening devices and then by shouting, determined that several survivors remained trapped under Juarez Hospital.

Lt. Raul Chavez of the Metro Dade Fire Department, one of a group of Miami-area volunteers in the rescue operation, said Mexican authorities had sought to abandon the effort there earlier but were persuaded to allow rescue workers to continue trying.

"People wanted to tear everything down, and now they know people are in there and they're trying to get them out," he said.

Chavez said relief operations were hindered by lack of coordination among Mexican authorities and specialists of various nations trying to help, each with his own idea of how to proceed. As he spoke, a Venezuelan expert was making a suggestion to the Mexican engineer in charge and a French fireman was trying to understand cries from a Mexican rescue worker seeking a pickax.

French and American experts walked off the rescue site in anger yesterday. Chavez said Mexican authorities allowed a group to work atop the rubble while members of the Miami team were burrowing inside in search of survivors. This created risk of a cave-in, endangering their lives, he added.

The French and Americans were back on the job today, however, joined by Venezuelans with special saws to hack through cement.

More than 700 patients, doctors and nurses were believed to have been inside the hospital when it crashed into a heap of wreckage during the earthquake. Most of their bodies have been removed.

The final death toll has been estimated much higher than the 4,500 bodies police announced had been recovered, because the exact number of corpses still lying beneath the rubble has not been determined. In addition, various Mexican agencies have issued different counts.