STEVENSVILLE, Md. -- Pennsylvania and other states around the Chesapeake Bay pledged Friday to cut in half the amount of phosphorus used in home lawn care by 2009.

The agreement, signed on Kent Island on the shore of the bay, accompanied announcements by two major fertilizer and pesticide producers to halve phosphorus in products they sell nationwide for private use.

The companies, Scotts Miracle-Gro Co. of Marysville, Ohio, and Lebanon Seaboard Corp. of Lebanon, Pa., said they would start reducing phosphorus in their products this fall, meaning gardeners would likely see the low-phosphorus products on shelves in the spring.

The agreement -- signed by Maryland, the District of Columbia, Pennsylvania and Virginia -- does not require all manufacturers to abide by the lower phosphorus levels. But the two companies already involved represent about half the residential market, and a Scotts Miracle-Gro official said Friday that other manufacturers would likely follow suit.

"By 2009, everyone else will be" using the lower levels, said Rich Martinez, chief environmental officer for Scotts.

The agreement did not specify any requirement for fertilizer producers to reduce phosphorus, nor did it say what would happen if the state reductions aren't met.

Phosphorus runoff from lawns contributes to pollution in the Chesapeake Bay. States on the bay have agreed to try to reduce pollutants like phosphorus by 2010.

"We took it for granted that the tremendous bounty of God's creation would always be there," said Virginia Gov. Tim Kaine at Friday's ceremony. "We haven't paid the attention we needed to the health and cleanliness of the bay."

Maryland Gov. Robert Ehrlich also acknowledged that bay cleanup efforts haven't moved as quickly as some hoped.

"There is a sense of immediacy here, and we need to get going," he said.

Pennsylvania Gov. Ed Rendell did not attend the signing, sending a staff member to sign the lawn products agreement for his state.

An environmental watchdog who attended said the agreement was a good idea, but that the region's states are far from meeting bigger goals. William Baker, head of the nonprofit Chesapeake Bay Foundation, said the region since 2000 has reduced 37 million pounds of nitrogen runoff per year, much lower than the goal of reducing runoff by 110 million pounds per year.

"We're 3 1/2 years away from the deadline," Mr. Baker said.

He said environmentalists are waiting to see if state governments set aside enough dollars to pay for improvements, such as paying to help farmers reduce pollution runoff.

"The proof will be in the state budgets," he said, adding that home lawn care isn't as big a threat to the bay as agriculture.