Federal safety officials yesterday issued a strong warning against letting children younger than 2 years old sleep in bed with their parents, setting off a new debate over whether the increasingly popular practice puts children at risk of suffocating.

The Consumer Product Safety Commission warning about "co-sleeping" was prompted by a new CPSC study that found the practice causes about 15 deaths a year.

"There is some evidence to suggest that the practice [of co-sleeping] may introduce a hazard of death by overlying" with a parent rolling on top of the baby, or next to it and smothering him or her, said the CPSC study, which reviewed death certificates nationwide from 1990 through 1997. As a specific cause of death, some certificates said "found under parent," or "accidentally rolled over by mother."

A number of prominent co-sleeping advocates--who encourage bed-sharing as a way to promote breast-feeding and increase bonding between parent and child--immediately criticized the CPSC warning.

James J. McKenna, a biological anthropologist who has done extensive studies in bed-sharing and is one of its strongest proponents, said the CPSC's conclusions were based on incomplete and anecdotal evidence that relies solely on the subjective opinion of medical examiners who filled out death certificates. The findings ignore studies that show that "even in the deepest stages of their sleep, mothers respond within seconds to a strange noise, sudden movement, grunt or cough of their co-sleeping infant," McKenna said.

Pediatrician William Sears, who endorses co-sleeping in his best-selling guide, "The Baby Book," agreed. "If you look at the data very carefully, you can conclude that more infants die alone in cribs than die in a parent's bed," Sears said. There are 2,705 deaths a year from sudden infant death syndrome (SIDS), Sears said. "There is no doubt in my mind that an infant is at less risk of SIDS if he sleeps with a parent," Sears said.

Sears stressed that bed-sharing must be done safely: Babies should be placed on their backs, on a hard firm mattress--not on a couch or waterbed; no other siblings should be in the bed and parents should not smoke or be under the influence of drugs, alcohol or anything that may suppress their ability to be aware of their babies and quickly respond.

The CPSC's position goes beyond that taken by any other government entity. The National Institute of Child Health and Human Development said more studies are needed before concluding that all babies should be kept out of adult beds. But parents should be aware of the possible hazards, officials said.

The issue of bed-sharing has also been contentious for the American Academy of Pediatric's task force on infant positioning and SIDS. The task force recently declined to take a firm stand against bed-sharing, but decided instead simply to warn parents about the possible hazards, said task force chairman John Kattwinkel.

Ann Brown, chairman of the CPSC, said her agency decided to take a harder stand based on the data collected by its staff, which showed that the number of infant deaths in adult beds is higher than the 50 deaths caused annually when babies are entrapped in their cribs and suffocate, mostly due to defects or broken parts in older cribs.

The study, released yesterday at an American Medical Association briefing, is the first to quantify the number of fatalities resulting from co-sleeping, said the commission, which has been active in a number of issues aimed at decreasing infant deaths, such as improving crib safety.

According to the CPSC data, 515 infant deaths occurred in adult beds from 1990 through 1997. Of these, 121 were caused by co-sleeping, with 77 percent of these deaths occurring in infants younger than 3 months old. While earlier studies said most overlying deaths occurred on waterbeds, the CPSC study found only 11 percent of the incidents involved waterbeds. And while an earlier study suggested that alcohol consumption was involved in a significant number of cases, the CPSC study found only two incidents (0.2 percent) where prior alcohol or drug consumption was reported.

The remaining 394 deaths were due to suffocation or strangulation, caused by the entrapment of the baby's head in various parts of the bed, or by placing the baby face down on a waterbed mattress.

"An adult bed is a dangerous place for a baby," Brown said. "The only safe place for babies is in a crib that meets current safety standards and has a firm, tight-fitting mattress. Place babies to sleep on their backs and remove all soft bedding, pillows and stuffed animals."

Parents who want to sleep with their babies should put a crib or bassinet "right next to their bed" to get the "benefits of bonding and breast-feeding with all the protection," she said.

A study of a recent two-week period found that half of all infants spend at least some part of the night in an adult bed, officials said. About one in six parents said their babies spent half or more of their sleeping time on an adult bed or mattress.