DALLAS - Millions of pounds of dangerous chemicals, including almost 40 tons of known or suspected cancer-causing agents, fouled the state's air this year as a result of plant mishaps, state records show.

"Anything like this is of concern," said Herbert McKee, a former Texas Air Control Board member who now heads the environmental control division of the Houston Health Department.

According to records examined by the Dallas Morning News, most of the emissions occurred in the Houston area, the center of the state's huge petrochemical industry.

The chemicals ranged from more than 46 million pounds of carbon monoxide, a common air pollutant, to 45 pounds of hydrogen cyanide, which can be deadly in concentrations as low as one part per 10,000.

Other chemicals that escaped this year included hydrochloric acid, sulfur dioxide, ammonia and chlorine, the newspaper said Sunday.

McKee and other officials say Texas could suffer a disastrous chemical leak such as the one at a Union Carbide plant in Bhopal , India, that killed more than 2,000 people, or the pesticide leak at a Union Carbide plant in Institute, W.Va., in August that hospitalized more than 130.

"I'm amazed, really, that we don't have more accidents like Bhopal or Institute," said Jerry Crowder, an associate professor of environmental engineering at the University of Texas at Dallas. "But the potential is definitely there."

Texas Air Control Board records show that some of the nation's largest oil and chemical companies - including units of Union Carbide, Dow Chemical Co., Shell Oil Co., Chevron Corp., Exxon Corp. and Diamond Shamrock Corp. - are among those responsible for the dangerous emissions.

Spokesmen for the companies and for the Chemical Manufacturer's Association defended the industry, saying it has an exemplary record.

"You can't eliminate the risk. Hazards are part of the chemical industry. But what we can do is reduce the risks," said Ed Van Den Ameele, Union Carbide's manager of media relations.

Tim Scott, spokesman for Dow Chemical USA's plant in Freeport, the largest petrochemical complex in the nation, said emissions from the plant - which included 14,000 pounds of chlorinated hydrocarbons, which are suspected carcinogens - "have had no impact on the safety of our workers or the environment."

Scientists say it is difficult to assess the health effects of toxic air emissions in Texas.

"The chronic effects are our biggest worry," said Bob Love, chief of the Air Control Board's emissions inventory system. "No one knows for sure what happens when humans are exposed to small amounts of these toxic substances over a long period of time.

"We know there are effects," he continued. "How severe they are, we don't know with any certainty. Therein may lie the biggest danger."

Despite the concern of state officials, efforts to regulate toxic emissions are in their infancy.

The Air Control Board has had the power to fine companies that violate its regulations against accidental emissions only since Sept. 1. None has been fined yet, board officials said.

And the reports filed by companies on accidental emissions have been on file in a computer for only a year. The computerized system allows air control officials to track the records of individual companies, specific chemicals or clearly defined areas of the state.

"Until last November, these reports would come in, and they'd gather in a pile each year," said Love. "Then a summer temporary employee would file away as many of them as he could for three months. Then they'd collect in a pile again until the next summer."

State officials said the emission reports filed by companies probably reveal only a fraction of the problem.