A lot of people have changed the way they wash clothes, and environmentalists say the Chesapeake Bay is a cleaner place because of it. Environmentalists lobbied for years to have the bay's watershed jurisdictions -- Maryland, Virginia, the District and Pennsylvania -- enact bans on phosphates in laundry detergents, arguing that they promote growth of algae that rob other aquatic life of essential sunshine and oxygen. Phosphates, compounds of the naturally occurring element phosphorus, are added to granular detergents as a water softener. There were hard-fought campaigns in Maryland, the District and Virginia, with the phosphate and laundry-soap industries spending thousands of dollars on lobbying efforts to defeat a ban, arguing that they would mean higher costs for consumers and dirtier laundry. No sale. Maryland's ban took effect first, in December 1985; last year, the state's three-year prohibition was made permanent by the legislature. The District followed, in September 1986. Virginia prohibited most phosphates as of Jan. 1, 1988. The result, according to official reports, has been to cut by one-third the amount of phosphorus going into sewage plants, to reduce the amount of phosphorus going into the bay, and to lower the expenses of the sewage treatment plants that remove phosphorus. There have been no reports of consumers sneaking into other states to buy phosphate-loaded detergents. "The scientific and public consensus" is that bans "have been a relatively cheap way to make improvements," said Russ Baxter of the Chesapeake Bay Foundation, an environmental lobby group. "They apparently have been wildly successful." In Maryland, according to a recent report by the state Department of Environmental Management, the ban reduced by 1,741 pounds per day the amount of phosphorus flowing into the bay from sewage treatment plants, a 45 percent decrease. Plants that remove phosphorus from their effluent are saving $558,600 a year, the report said. In Virginia, according to the State Water Control Board, the phosphorus level in wastewater discharged from sewage treatment plants has dropped by an average of 50 percent from 1987 levels. The phosphorus flowing into the plants dropped by more than 30 percent -- a higher level than the 20 to 30 percent level that officials had predicted. One major goal of environmentalists remains unfulfilled: Pennsylvania, which is home to three major phosphate manufacturers, has no phosphate ban. A move to have the state legislature enact one faces a tough fight, said Tom Sexton, executive director of the Chesapeake Bay Foundation's Pennsylvania office.