Senate and House versions of clean air legislation differ greatly on provisions that will affect the chemical industry profoundly.

The House Energy and Commerce Committee overwhelmingly approved its version late Thursday. The bill is expected to be passed with few changes by the full chamber next month. The Senate approved its own clean air bill earlier last week.While last-minute revisions in the bills centered on sections that would reduce acid rain and urban smog, less dramatic changes have produced two

broadly different sets of rules to cut toxic air pollution. As with other differences in the bills, the air toxics sections will be reconciled by a conference committee of both chambers, sometime after the House passes its clean air bill in May.

When that work begins, lawmakers will be faced with two concepts of air toxics regulation, reflecting the two approaches that have dominated debate on the matter for the last several years.

In the Senate, members have passed rules that establish rigid guidelines for industry, defined in hard numbers. After a first round of reductions in toxic pollution from chemical plants, the Senate bill would define what is an ''acceptable risk" from cancer. This risk is defined as no more than one chance in 10,000 of contracting cancer from lifetime exposure to toxic air pollution, and a stated goal of reducing risk to one in 1 million, a widely accepted definition of "negligible risk."

In the House bill there are no such definitions of risk. Instead, the bill defers to present law and future action by the Environmental Protection Agency, which would be given broad responsibility to decide how much the law will eventually reduce air toxics, and how much it will cost industry.

The chemical industry fought to keep hard numbers on risk out of the bill, arguing that it would be arbitrary to apply them uniformly to the hundreds of toxic chemicals that will be regulated by the strengthened Clean Air Act.

In general, the House version of the bill avoids setting rigid guidelines for air toxics like those the Senate chooses for "acceptable risk." In the Senate bill, any chemical plant unable or unwilling to reduce chemical emissions so they are below the one-in-10,000 risk standard would automatically be forced to shut down. The House version contains no such plant-closing rule. Industry opposed the rule.

While the House clean air bill is generally preferred by industry, there are a few areas where the Senate bill is better, says William Fay, chairman of the Clean Air Working Group, the leading industry lobby.