The Maryland House of Delegates, responding to appeals to enhance the Chesapeake Bay restoration effort and reacting against an intense lobbying effort by industry, approved legislation tonight that would ban the sale of phosphate detergents for a three-year period beginning in July.

The House's 79-to-48 vote for a measure that is significantly weaker than an earlier version approved by the Senate capped one of the 1985 session's most contentious debates and virtually guarantees that Maryland will join six other states that have banned phosphate detergents from supermarket shelves.

Differences between the House version -- which incongruously would exempt about 35 percent of the state's population from the ban while prohibiting them from purchasing the products within the state -- and the measure passed by the Senate nearly a month ago will have to be reconciled by a conference committee.

Jubilant supporters of the measure proclaimed tonight's vote a victory for both the environment and the General Assembly's ability to resist special interest pressures.

"Obviously we are elated," said Del. Robert G. Kramer (D-Anne Arundel). "It's a testament to the House, which was faced with 20-plus lobbyists working to defeat the bill."

Kramer's estimate may have been inflated -- no one seems quite sure how many lobbyists from either side worked the bill -- but there was little doubt that the perception of a piling-on effect by soap manufacturers, detergent associations, phosphorous mining companies and textile firms took its toll.

"The lobbyists turned people off," said Del. Paul Weisengoff (D-Baltimore). "There was a lot of overkill and they strong-armed a lot of people."

Proponents tonight fought off another series of amendments designed to cripple the phosphate ban by exempting even more people than were previously excused under amendments added by a House committee. As currently written, the legislation exempts homeowners with septic systems, commercial and coin-operated laundries, hospitals and veterinary clinics, among others.

Despite the exemptions and the apparent inconsistency that prohibits those who are exempted from purchasing phosphate detergents, state Natural Resources Secretary Torrey C. Brown said the legislation would be "enforceable" if enacted in its current form.

The exemptions, which supporters of the legislation will seek to have stripped during the conference committee, "might make it uninterpretable, but not unenforceable," said Brown. "The bill is very complementary to all of the other efforts" to clean up the bay that were enacted in 1984.

Opponents of the bill fought a losing battle tonight on grounds ranging from criminality to dirty laundry.

Attempting to deride a bill that Del. Michael H. Weir (D-Baltimore County) labeled a "knee-jerk reaction to a bunch of environmental kooks," they raised the specter of Natural Resources police officers "lurking in the bushes" on the D.C.-Maryland line, waiting for bootleggers of phosphate detergents.

They proclaimed it an affront to homemakers who Del. Martha Klima (R-Baltimore County) said would be unable to "do an adequate job on our linen and our diapers."

And finally, they predicted it would backfire on legislators facing reelection in 1986. Soap and Detergent Association lobbyist Devin Doolan said constituents "will be asking these folks a lot of questions when they see how bizarre and inconsistent this is."

But little of that mattered to supporters of the 1985 session's major piece of environmental legislation.

Said Del. Thomas A. Rymer, a Democratic legislator from southern Maryland: "People who live and fish on the bay have known for a long time that it's going downhill. Let's stop playing games with this bill."