LITTLE ROCK, Ark. (AP) — Northwest Arkansas city officials have asked the Environmental Protection Agency to delay a new regulation that would implement a stricter standard for phosphorus discharges.

Regional officials said the regulation — which is 10 times stricter than the current level — would require costly modifications at six wastewater treatment plants in the area. They visited Washington in recent days to meet with EPA officials and members of Arkansas' congressional delegation.

The regional officials want the EPA to wait to implement the rule until studies by the agency and by the University of Arkansas have determined if the new rule is even needed.

David Cameron, the city administrator for Siloam Springs, said the EPA must consider the affect of the new rule on the region's growing economy as well as efforts already made and money already spent to address the phosphorus discharge issue.

"We have an obligation to protect the environment," Cameron said. "We just want to make sure it's done fairly."

Cameron joined Bentonville Mayor Bob McCaslin, Fayetteville Mayor Lioneld Jordan, Rogers Mayor Steve Womack and Springdale Mayor Doug Sprouse on the trip to Washington.

Cameron said the hope was the group effort would make an impression on EPA officials and that they came away encouraged after their meeting even though agency officials made no promises.

"We also heard in several meetings that this administration will be emphasizing and supporting regional strategies around the country," McCaslin said. "That approach certainly matches how we've been working in Northwest Arkansas for many years and we are very pleased to hear that federal policy is moving in this direction as well."

The U.S. Supreme Court ruled in 1992 that Oklahoma could establish its own standards for phosphorus in the Illinois River — which starts in Arkansas and flows into Oklahoma — and force Arkansas to lower the phosphorus amounts sent downstream into Oklahoma. Oklahoma set its limit at 0.037 milligrams per liter in scenic rivers such as the Illinois.

The EPA wants to reduce allowable phosphorus emissions from 1 milligram per liter, the current standard, to 0.1 milligram per liter at a regional sewer plant that will open next year and will be operated by the Northwest Arkansas Conservation Authority.

Regional officials say a 2003 agreement between Oklahoma and the five Arkansas towns specifies a 1-milligram standard. Cameron said the towns already have spent $250 million to $300 million since then to upgrade and build sewer treatment facilities.

Regional officials say that if EPA requires existing plants to meet the 0.1-milligram standard, it will cost millions of dollars, which would have to passed along in rate increases.

"As the permits for existing wastewater treatment plants in Northwest Arkansas expire and the June 2012 date for compliance with Oklahoma's phosphorus standard approaches, a comprehensive strategy is needed to address nutrient impairments in the Illinois River watershed in both states," EPA spokesman Dave Bary said in a written statement.