A House committee tonight substantially weakened legislation to ban phosphate detergents in Maryland, sending to the full House a heavily amended measure that one soap industry lobbyist said "exempts everything but a one-armed paper hanger."

After working for three hours on a relatively stringent bill that had earlier passed the full Senate, the House Environmental Matters Committee approved on an 18-to-6 vote legislation that bans the sale, use and distribution of phosphate detergents, but exempts from the prohibition homeowners with septic systems, coin-operated and commercial laundries and federal government facilities.

The vote tonight represented at least a tactical victory for the small army of lobbyists who have turned the phosphate bill into one of the most heavily lobbied -- and expensively fought -- measures to pass through the General Assembly in many years.

"A lot of vodka went into those amendments," said a delighted Ira C. Cooke, who was retained by the Procter & Gamble company to defeat the bill.

"It looks like a giant Christmas tree," said Devin J. Doolan, lobbyist for the soap and detergent association, arguing that the amendments would convince the House that the ban is an unworkable and misguided attempt to improve water quality in the Chesapeake Bay and should die.

Committee chairman Larry Young (D-Baltimore), who estimated that as many as 15 lobbyists had been active representing clients on the phosphate ban, most of them hired by industries opposed to the legislation, conceded that his panel had passed "a weak bill."

Asked about the apparent contradictions in the bill adopted by his committee -- people who own septic tanks may use phosphate detergents, but cannot purchase them in Maryland -- Young replied: "You're not asking me to comment on the wisdom of my own committee, are you?"

Del. Paula Hollinger (D-Baltimore County), a strong advocate of the ban, said, "There are amendments there I don't like, but the basic concept of the ban is intact."

The Senate sponsor of the bill agreed. "I don't have major problems with what they did," said Sen. Gerald W. Winegrad (D-Anne Arundel). "I think the bill is still strong and will assist in the effort" to clean up the Chesapeake Bay.

How the amended bill will fare on the House floor, and if passed, in conference with the Senate, is uncertain. "The debate now goes to the floor." said Young, "Where it goes from there is anyone's guess." But industry lobbyists who have turned on relentless pressure to kill the legislation were wearing smiles tonight.

The intensity of the lobbying effort launched by Doolan and his comrades representing soap companies, phosphorous producers and chemical companies reached a fever pitch today, with proponents of the ban suggesting darkly that an afternoon meeting between the lobbyists and House Speaker Benjamin L. Cardin had turned the tide against the bill.

Cardin has maintained a neutral position on the legislation, a point that Young reiterated to his committee today when he called them into his office to defuse an atmosphere he said was "getting very ugly."

"The pressure has been awesome," said Young. "The lobbying has been the most difficult I've undergone in my 11 years here."