Using all the props associated with a brand-X-versus-brand-Y commercial, the soap and detergent industry plans to conduct a consumer study in the District to prove that dirty laundry will at best become dingy if a phosphate detergent is not used.

The City Council's Public Works Committee was prepared to vote last week in favor of a bill proposing a partial ban on the sale and use of cleaning agents containing phosphates, figuring the city could save $1.5 million to $2 million a year by not having to remove phosphorus from waste water.

But the committee delayed action for two weeks at the request of Carol Thompson, director of the city's Department of Consumer and Regulatory Affairs, who said the industry should be allowed to conduct a study.

The Soap and Detergent Association, at the urging of Procter & Gamble Co., came up with the idea of the study, which it hopes will buttress its argument that without phosphates, consumers will end up spending more money to buy extra detergents and additives to get their clothes clean.

Manufacturers add phosphates to detergents to improve cleaning performance. Environmentalists argue, however, that phosphates promote the growth of nuisance algae in waters such as the Potomac River and Chesapeake Bay, leading to a decline in water quality.

The proposed study calls for a group of District residents, armed with dirty laundry, to meet home economists at laundromats throughout the District.

"In the laundromat, the consumers will be given soiled garments, which shall be split in half," according to proposed guidelines for the study. "The consumers will put one-half of the soiled garment in with a load of their own laundry and wash with their nonphosphate detergent. The other half of the soiled garment shall be put in with a second load of the consumer's dirty laundry and will be washed with a leading phosphate detergent."

The guidelines point out that either Tide or Cheer, the best-selling phosphate detergents in the District, would be acceptable for the study.

According to the guidelines, the home economists conducting the study will be selected by the city's consumer department and by Procter & Gamble.

Louis Sernoff, an attorney representing the soap industry, said the study will demonstrate that consumers may have to use additional detergent, bleach and hotter water to get their clothes clean without phosphates. Although the committee delayed its action only two weeks, Sernoff said it will take about two weeks to work out the full details and about a month to complete the study.

When she read the proposal for the study, City Council member Hilda Mason (Statehood-At-Large), who introduced the phosphate bill, shook her head.

"It is ridiculous," said Mason. "They can just come to my house and see me do my laundry. I think this is just a stall to try to get enough votes to kill the bill."

Last year, Maryland adopted a three-year ban on the use of phosphates despite a massive campaign conducted by detergent manufacturers' lobbyists. Environmentalists fear that the District consumer study is the first sign that an intensive lobbying campaign will unfold here.

Ann Powers, vice president of the Chesapeake Bay Foundation, said a consumer study will not provide any additional information. "The industry is just trying to pull the same high-pressure tactics they used in Maryland," she said.