Chemical manufacturers are generally pleased with the House version of clean air legislation because it has less stringent standards for toxic pollution controls than the bill the Senate passed earlier this year.

But the industry prefers two important provisions in the Senate version and will push for their adoption in the congressional conference to reconcile the two bills.The House voted 401-21 late Wednesday to approve the comprehensive bill, which would reduce acid rain pollution, and urban smog, as well as toxic air pollution.

Mark Nelson, a legislative affairs expert for Du Pont Co. in Washington, said the House bill gives chemical manufacturers more flexibility in choosing mechanical pollution controls to reduce toxic air pollution.

Both the Senate and House versions say that chemical companies must use the "maximum available control technology," to control hundreds of cancer- causing chemicals, but define that term differently.

Both bills require that the "maximum available" control technology be defined as the technology used on the best-controlled plants for a particular chemical. The Senate bill would average the emissions for the best-performing 10 percent of plants that make a toxic chemical, and set the level of emissions from that 10 percent as the standard for all makers of that chemical.

The House version would use an average of the top 15 percent of the plants, which would likely result in a looser pollution standard.

The House version of the bill also would take cost into consideration in determining what the "maximum available" technology is and perhaps ensure that an economically infeasible technology is not chosen as the industry standard, said Mr. Nelson. The Senate bill makes no references to the cost of technology.

After the first, large reductions in toxic pollution are made under the clean air plan, both the Senate and House legislation deal with the "residual risk" from the remaining proportion of chemicals still being released into the air.

The Senate bill would use a mathematical estimate of cancer risk to establish this second round of reduction standards, with a 1-in-10,000 risk of cancer being the maximum level of risk and 1-in-1 million being the goal of the regulations.

Mr. Nelson said this approach to residual risk is too arbitrary, and he said the industry favors the House bill, which would leave most of the responsibility for this standard to theEnvironmental Protection Agency and the Surgeon General.

The two Senate provisions preferred by the industry would give manufacturers credit for voluntary reductions in toxic pollution, presumably made without expensive controls, and allow companies to alter their production processes without having to install new controls.