WASHINGTON - The best inventory of toxic chemicals that Houston-area industries discharge to the air may be crammed into a House subcommittee's filing cabinets, not stored in the computers of the Environmental Protection Agency or the Texas Air Control Board.

EPA concedes its data base is poor, with no continuing, comprehensive effort to collect that information.

Despite requests by Texas officials that companies report how much they release of specific toxic substances, the state's statistics are still largely confined to a broad group of pollutants that includes many toxic chemicals, but others that are less hazardous, too.

When Rep. Henry Waxman, D-Calif., wrote 86 chemical companies last year to ask what amounts of specific toxic substances they release to the air, the Health and Environment Subcommittee that he chairs said no government agency had tried to gather the information before.

Twenty-nine companies with plants in Harris, Galveston, Brazoria, Orange and Jefferson counties responded. In 1984, they released or had permits to release about 10 million pounds of 45 of the chemicals Waxman asked about.

Releases of 16 known or suspected cancer-causing agents totaled more than 2.5 million pounds - from 553 tons of benzene to less than 200 pounds of trichloroethylene.

The total included about 6 million pounds of 22 substances EPA says can be immediately dangerous in a big enough accident - releases ranging from 1,960 tons of ammonia to about two pounds of hydrogen fluoride.

Some releases were chemicals fitting both categories. They included 206 tons of acrylonitrile, more than 83 tons of chloroform and more than 10 tons of formaldehyde.

Fifteen companies gave totals for all releases, routine and accidental. Eight gave partial information, including five that told only about accidents. Six provided no information on amounts released. Some companies extensively described safety and health surveys and control equipment. Others did not.

The inquiry was part of an investigation of chemical industry practices after methyl isocyanate gas leaked from a Union Carbide plant in Bhopal , India, killing more than 2,000 persons. Waxman wanted to know about releases of that chemical and 18 others Union Carbide considers "extremely hazardous," any others with similar dangers, and 37 substances EPA was considering for regulations because of possible hazards from breathing them over long periods.

What the panel received, said one staff member, was "very sketchy information. We never pretended to have anything comprehensive. But the picture we do have is very alarming. It's only the tip of the iceberg."

Bill Becker, who heads the national organizations of state and local air pollution directors, said the companies' responses to the committee show "we just don't have the information in hand, from a national perspective, to confidently proclaim what's being emitted."

Bern Steigerwald, an EPA air official, acknowledged the agency needs to learn more about industry's toxic air releases, but said getting data like Waxman's is only "one small part" of defining the problem. "You can blow a lot of money putting samplers out," he said.

The subcommittee staff member said some companies' "haphazard response" indicates "the haphazard care given to these chemicals by the chemical industry. If they give erroneous or incomplete information, it implies they don't know themselves about what they're putting into the air."

Several companies with plants in this area told the panel they could not provide information about releases of specific chemicals, because neither EPA nor Texas officials had ever asked for it.

Union Carbide, for example, disclosed volumes of individual chemicals released by its West Virginia plants because that state had required the information, but not the releases at its Texas City facility. Uniroyal said monitoring and measuring releases of all individual chemicals would be "impractical, if not impossible." Amoco said information about releases of specific chemicals was "seldom of interest."

Critics of EPA's progress in controlling specific substances contend one problem is that release data are generally not collected for unregulated chemicals, and the resulting lack of information has slowed the setting of regulations.

Nonetheless, the companies insisted their handling of toxic chemicals is far from haphazard and represents a steady commitment to the wellbeing of plant workers and the public around the plants. Several said toxic chemicals measured in the air just outside plants are far below levels the federal government allows workers to breathe.

A Monsanto Co. executive told the panel the "raw data" his company provided indicate nothing but the amounts of substances that are released.

"Understanding how these data may relate to potential human exposures and associated health risks, if any, is quite another matter, requiring a completely different kind of scientific evaluation. Our scientists and our expert consultants follow this issue closely and, based on everything we've seen, we are convinced that the air emissions from our operations pose no health problems for our employees or the citizens in our plant communities."

Dow Chemical Co. urged that "a clear distinction" be made between long-term health risks of "normal" releases from vents in a chemical process and immediate dangers of an accidental leak of a highly toxic material. "The appropriate control strategy for acute risks will often be markedly different than the appropriate control strategy for chronic risks."

Shell Chemical Co. was typical in its description of extensive controls including incinerators, scrubbers to neutralize chemicals, seals for pumps and compressors, and flares to burn gases from vents. Relief valves make non-routine releases "to ensure worker safety and protect equipment from explosions and fires," the company said.

Celanese Corp. said failures in safety systems would "normally" be detected. That company, among others, downplayed the likelihood of a Bhopal -type disaster in this country. An internal Celanese memorandum explained its safeguards to prevent a "worst-case" accident.

"Wind directions, in most cases, happen to blow only a small percentage of the time in those directions where communities could become involved," the memo said. "The incident at Bhopal , however, has taught us that Murphy's Law governs and those worst cases have been presented."