The federal government is promising to crack down on pollution from factory farms and urban stormwater that harms the Chesapeake Bay - that is, unless the states do it first.

The federal government is offering the wiggle room after Maryland, Virginia and Pennsylvania officials complained about potentially far-reaching new regulations on their farmers.

"The states generally believe they have a lot of local knowledge. They have a lot of programs working well. They would like the first shot at constructing new regulatory regimes," said Chuck Fox, a top U.S. Environmental Protection Agency official for bay...