The Biden administration on Tuesday strengthened limits on smog-forming pollution from buses, delivery vans, tractor-trailers and other trucks, the first time in more than 20 years that tailpipe standards have been tightened for heavy-duty vehicles.

The new rule from the Environmental Protection Agency is designed to cut nitrogen oxide from the vehicles by 48 percent by 2045. Nitrogen dioxide is a poisonous gas that has been linked to cardiovascular problems and respiratory ailments like asthma. The rule will require manufacturers to cut the pollutant from their vehicles starting with the model year 2027.

But the new rule is not as stringent as one proposed by the E.P.A. in March, which would have cut the pollutant as much as 60 percent by 2045. And the agency stopped short of ​​requiring that truck manufacturers also cut greenhouse gas emissions associated with burning diesel fuel or convert their fleets to electric models.

That has disappointed many environmental activists, who said federal rules for vans, buses and trucks should match efforts in states like California and Washington that are intent on phasing out diesel fuel.

Michael Regan, the administrator of the E.P.A., said that regulations tackling greenhouse gas emissions from trucks would be issued in the spring. He said that releasing both rules together would have taken more time and he felt it was urgent to move quickly to limit nitrogen dioxide.

“It was important for us not to wait, but to move forward,” Mr. Regan said, noting that about 72 million people live within 200 meters of a truck route. Cutting pollution from trucks will prevent 3,000 premature deaths and as many as 3 million cases of asthma.

The action fits in the administration’s broader goal of trying to improve conditions for communities that are disproportionately burdened by pollution.

“We know that these garbage trucks, tractor-trailers, delivery trucks, they’re going through our neighborhoods and they are impacting children and families,” Mr. Regan said. He called the measure “very good when you think about the people in this country who are disproportionately exposed to diesel emissions and truck emissions.”

José Miguel Acosta Córdova is among them. Mr. Acosta Córdova, who lives in Chicago, said his family and neighbors suffered daily from asthma, heart conditions and other consequences of living near truck traffic that spills out of distribution warehouses. But Mr. Acosta Córdova, a senior transportation policy analyst at Little Village Environmental Justice Organization, said the new rule was not sufficient to help polluted communities like his.

California regulators this year have started discussing whether to require heavy duty fleet owners to transition to zero-emissions vehicles. Several other states have signed a multistate pact to require 100 percent sales of zero-emission trucks by 2050.

Trucking industry officials said the new rule would be costly, particularly for small truckers.

Jay Grimes, director of federal affairs for the Owner-Operator Independent Drivers Association, said the requirement that truck manufacturers cut emissions by 2027 was too aggressive.

He also maintained that any rules requiring cuts in greenhouse gas emissions would be costly, and the price was likely to be passed on to the average consumer.

“Certainly we all want cleaner air, but if independent and small business owners can’t afford the new trucks, they’re going to stay with the older trucks, which are not going to be as clean and efficient,” Mr. Grimes said. While new rule requires new models built after 2027 to be built with stronger nitrogen oxide pollution controls, it does not require truckers to stop driving older models.

Mr. Grimes said the cost of a new truck with pollution controls runs about $200,000, a price he said “for most of our members makes it hard for them to invest in new equipment.”

Mr. Regan said the E.P.A. was working with manufacturers to see if they could take advantage of federal tax credits for electric vehicles that are part of $370 billion in clean energy provisions under the Inflation Reduction Act.

Environmental activists said they worried the delay in issuing greenhouse gas rules for heavy trucks would make it harder to reach President Biden’s goal of cutting United States emissions at least 50 percent from 2005 levels this decade. With Republicans poised to take control of the House in January, the prospects are dim for more climate legislation, which has put pressure on agencies like the E.P.A. to execute Mr. Biden’s climate agenda through regulations governing power plants, automobile tailpipe emissions and oil and gas wells.

The agency is working on new limits for auto pollution that could accelerate a transition to electric vehicles and additional restrictions on industrial soot released by power plants. Mr. Regan pushed back against criticism that the agency was moving slowly and said a number of planned regulations would be issued by the spring.

Mr. Regan attributed some of the delay to the fact that agency officials have been analyzing the new law to better understand how the tax incentives can be optimally deployed. He suggested that some proposed rules might be more stringent than the agency initially envisioned because the tax provisions in the new climate law could enable industries to more quickly adopt technology that will draw down carbon emissions, allowing them to hit tougher targets.