WASHINGTON — The Trump administration on Monday took its first step toward tighter pollution controls on trucks, an anomalous move for a government known for weakening environmental policies but one that would pre-empt tougher state rules.

Andrew Wheeler, the head of the Environmental Protection Agency, began the legal and regulatory process for curbing highway truck emissions of nitrogen dioxide, which has been linked to asthma and lung disease.

While the move could give President Trump a nominal environmental achievement for the 2020 campaign, public health experts say the truck regulations are not as out of line with administration policy as they would appear. The emerging rule will quite likely limit nitrogen dioxide pollution more than current standards, they say, but still fall far short of what is necessary to significantly prevent respiratory illness and even premature deaths.

Instead, the administration appears to be complying with the wishes of the trucking industry, which has called for a new national nitrogen dioxide regulation to override states that could otherwise implement their own, tighter rules. On that front, the E.P.A. rule is likely to open a new battle in Mr. Trump’s long-running war with California over environmental regulations and states’ rights. California is already moving ahead with stringent state-level standards on nitrogen dioxide pollution from trucks that could be replicated by other states.