YOU WOULD HOPE that any true-to-the-bay state legislators in Maryland would think twice before voting against an important bill to help clean up the waters there and elsewhere. But some members of the House of Delegates apparently are still falling for the detergent lobby. The bill would ban phosphates from detergents and, supporters say, would substantially cut the amount of phosphorus being discharged into the Chesapeake Bay. Gov. Harry Hughes and the state Senate -- by a solid 39-to-5 vote -- favor the phosphate ban, and thoughtful members of the House agree.

But members of the House Environmental Matters Committee and any other delegates willing to listen are being urged by the lobbyists to kill the bill. All sorts of flimsy grounds are being cited. One is that the bill's impact would be limited. But is that a sound reason for not doing anything in this session? Another argument by the opponents is that phosphates improve the cleaning power of detergents. Maybe so, but phosphates also strengthen the killing power of water, by increasing the growth of algae that then die and decrease the supply of dissolved oxygen. Result? The killing off of submerged vegetation, shellfish, finfish and other things universally deemed good for the bay.

Six other states have recognized the good sense of a phosphate ban. So have Akron, Dade County, Fla., and Chicago. Supporters of the ban say that half the population of the country is doing just fine with phosphate-free detergents. Maryland, of all places, should be eager to embrace every legislative protection possible for the Chesapeake Bay. The ban on phosphates is clearly in this category, and it deserves the vote of every House member who is serious about saving the bay for future generations.