The Environmental Protection Agency said Wednesday that it would uphold drinking water standards for two harmful “forever chemicals,” present in the tap water of millions of Americans. But it said it would delay deadlines to meet those standards and roll back limits on four other related chemicals.

Known as forever chemicals because of their virtually indestructible nature, PFAS are a class of thousands of chemicals used widely in everyday products like nonstick cookware, water-repellent clothing and stain-resistant carpets, as well as in firefighting foams.

Exposure to PFAS, or per- and polyfluoroalkyl substances, has been associated with metabolic disorders, decreased fertility in women, developmental delays in children and increased risk of some prostate, kidney and testicular cancers, according to the E.P.A.

President Joseph R. Biden Jr. had, for the first time, required water utilities to start bringing down levels of six types of PFAS chemicals to near zero. He set a particularly stringent limit of four parts per trillion for two of those chemicals, called PFOA and PFOS, which are most commonly found in drinking water systems.

The Trump administration said it would uphold the limits for those two types of PFAS, but would delay a deadline for water utilities to meet those limits by two years, to 2031.

The E.P.A. said it would rescind the limits for the other four chemicals.

“We are on a path to uphold the agency’s nationwide standards to protect Americans from PFOA and PFOS in their water,” Lee Zeldin, the E.P.A. administrator, said in a statement. “At the same time, we will work to provide common-sense flexibility in the form of additional time for compliance,” he said. “EPA will also continue to use its regulatory and enforcement tools to hold polluters accountable.”

The move to weaken some PFAS limits came after trade groups representing the chemicals industry, as well as water utilities, had challenged the Biden-era limits, saying they created an impossible standard that would cost municipal water agencies billions of dollars to meet.

The chemicals are so ubiquitous that they can be found in the blood of almost every person in the United States. Government studies of private wells and public water systems have detected PFAS chemicals in nearly half the tap water in the country. In 2022, the E.P.A. found the chemicals could cause harm at levels “much lower than previously understood” and that almost no level of exposure is safe. In 2022, the E.P.A. found the chemicals could cause harm at levels “much lower than previously understood” and that almost no level of exposure is safe.