House Energy and Commerce Committee Chairman John D. Dingell (D-Mich.) sided with the Reagan administration yesterday against strong new controls on toxic air pollutants. His opposition virtually kills a proposal motivated by the deaths of about 2,000 persons last December in Bhopal, India.

"I am concerned about the need for this new clean air regulatory bill, which stands apparently independent of the Clean Air Act," said Dingell, who warned that costs of the envisioned controls would be "staggering."

"One may ask why Congress, with its vast ignorance of scientific matters, is rushing ahead with this kind of unwise action," Dingell told an Energy and Commerce subcommittee headed by Rep. Henry A. Waxman (D-Calif.), the bill's chief sponsor.

Taking the stand moments later, Environmental Protection Agency Administrator Lee M. Thomas labeled the bill "impossible . . . its objectives unattainable."

"We'd have to set up another EPA as big as this one to deal with this act," Thomas said. "It would take nearly as many people as we have dealing with all other statutes -- 11,000 people -- and $1 billion a year."

Waxman, struggling to retain control over a hearing that threatened to disintegrate into a shouting match among panel members, said the bill is necessary because of EPA's "record of inaction" in controlling toxic emissions through existing laws.

"More than 60 million pounds of toxic chemicals are leaked or vented into America's air supply each year," he said. "For all but a handful of the dozens of air toxins, there are no government standards."

Rep. James J. Florio (D-N.J.), a cosponsor of the bill, said the agency has listed only six substances as hazardous air pollutants since being given authority in 1970 to control toxic emissions.

The measure, drafted in response to a chemical leak in Bhopal, would require the EPA to regulate 85 dangerous emissions from industries, cars and trucks and to monitor for hundreds more.

According to EPA estimates, about 2,000 Americans a year contract cancer from toxic industrial emissions.

"What this means is that the EPA is allowing the Bhopal tragedy to happen in our country each year," said Rep. Timothy Wirth (D-Colo.), who joined Waxman and Florio in denouncing a new EPA strategy that would assign the states much of the burden of regulating chemical plant emissions.

Thomas defended the new policy as an effective use of the agency's limited resources, saying routine emissions of toxics "do not necessarily pose a significant public health risk."

He also testified that the bill could have "serious adverse impacts" on society, eventually affecting hundreds of thousands of gasoline stations, residential and commercial boilers and sewage-treatment plants and possibly outlawing diesel engines by 1995.