A bill to ban phosphate detergents from supermarket shelves in Maryland resurfaced today and immediately touched off an acrimonious exchange between its chief sponsor and a soapmakers' representative.

The debate was not supposed to start until Thursday, when the bill comes before the Senate Environmental and Economic Affairs Committee. But after supporters finished their pitch at a press conference in a legislative hearing room, Devin Doolan, lobbyist for the Soap and Detergent Association, stormed the podium from a seat in back.

Doolan said environmentalists' contentions that a ban would cut the amount of phosphate discharged into the Chesapeake Bay by 13 percent were far higher than his scientists had figured. And he said the 4 to 5 percent reduction envisioned by his people "would unequivocally have no effect on water quality."

Sen. Gerald Winegrad (D-Anne Arundel), the bill's sponsor, shot back angrily, "Sure, it's just part of a combination of things we're doing to clean up the bay. But to argue that it isn't worth doing is just plain illogical."

Doolan and Winegrad then pleaded their cases before reporters.

"They soap manufacturers just want to flush it all down the drain and shift the burden for the cleanup to the sewage treatment plants," Winegrad said. State law will require large sewage treatment plants to remove phosphates from effluent by 1987.

"There isn't a shred of evidence that a phosphate ban would improve water quality one bit in the Chesapeake Bay," countered Doolan as the television cameras rolled, "and the state Health Department agreed with us on that three times before this."

Manufacturers add phosphates to detergents to improve cleaning performance. But environmentalists say the jazzed-up soap contributes one-third of the phosphorus going into public waste water treatment plants.

The bill, which would put Maryland in league with New York and five other states that have banned phosphates in laundry soap, was shelved last year. But this year, backers are buoyed by support from Gov. Harry Hughes, who withheld backing last year for fear that it might undermine support for his own Chesapeake Bay cleanup initiatives. With Hughes' initiatives now in place, his Health and Mental Hygiene Department announced today that it will back the ban at Thursday's hearings.

Phosphorus and nitrogen were identified in a $27 million federal study as the principal villains in the continuing decline of Chesapeake water quality. Excesses of these nutrients promote algae growth, which robs the bay of oxygen and decreases light penetration, killing valuable grasses, the study found.

Among the supporters of a phosphate ban here today were representatives of the Washington Suburban Sanitary Commission, sewer authority for Montgomery and Prince George's counties. The commission maintains that a ban would reduce its treatment costs by $2 million a year and cut its sludge production by 23,000 tons a year.

The soap manufacturers dispute that, maintaining that the biggest effect of banning phosphates would be $15 million a year in added costs for Maryland consumers -- for higher soap prices, more hot water and additives and washing machine repairs.