ANNAPOLIS, AUG. 26 -- The State of Maryland took the first step in its renewed pledge to cut the amount of harmful nutrients flowing into the Chesapeake Bay when it committed $28 million today for an "innovative" nitrogen removal system at a wastewater treatment plant on the Patuxent River in Prince George's County.

The state made good on its long-held promise to pay the cost of cleaning up the Patuxent, but is hoping that the federal government will eventually pick up part of the tab. The money committed today will go to the Washington Suburban Sanitary Commission for its five-year-old plan to construct a $38 million addition to its Western Branch plant in Upper Marlboro -- making it the largest treatment plant in the region to remove nitrogen from wastewater.

"We have an opportunity to show our commitment to cleaning up the Patuxent," said Gov. William Donald Schaefer. His aides described today's funding action by the three-member state Board of Public Works as an "unprecedented level of state support for nitrogen removal within the Chesapeake watershed."

Nitrogen and phosphorous are the nutrients that set off a biological reaction that eventually depletes oxygen in the water and can kill aquatic life.

They are derived from industry discharges, fertilizer runoff and sewage. Schaefer and officials from Virginia, the District and Pennsylvania agreed at a summit meeting in Norfolk this month to reduce the amount of nutrients flowing into the bay 40 percent by the year 2000.

Environmental officials said the action was especially important because the new plant will address the problem of nitrogen removal. Because the federal Environmental Protection Agency has held that nitrogen does not need to be removed from the discharge of most sewage plants, it has withheld important federal funding.

Environmental officials charged with restoring the Chesapeake disagree with the EPA position, and were heartened at the Norfolk meeting when EPA Administrator Lee M. Thomas said the agency will review its position.

Schaefer said the state was "gambling" that EPA will allow more than $10 million committed to the state for unspecified projects to be used for the project at Western Branch, already rated as one of the most effective treatment plants in the region. A letter from EPA regional administrator James M. Seif to the state's Department of Environment doesn't make any promises, but it acknowledges that "national attention is focused on the bay and our mutual effort to improve its water quality."

State Department of Environment Secretary Martin W. Walsh Jr. said that it was at a private meeting between Thomas and Schaefer that the idea of using the $10 million from the EPA was discussed. "That meeting in Norfolk is what put it {the project} to bed," Walsh said.

If the federal money is denied, the state will have to put up the entire $28 million, Schaefer said. He disagreed with the suggestion by a fellow Board of Public Works member, Comptroller Louis L. Goldstein, that residents of Montgomery and Prince George's counties pay more of the cost, saying that the state has agreed to pay for the cleanup costs and the Washington Suburban Sanitary Commission is already committing nearly $6.5 million to the project.

Walsh said that nitrogen becomes the "driving" nutrient in salty water, and its removal will have "major beneficial results" on the lower Patuxent and eventually the bay. But because it has been removed only at small sewage treatment plants in Virginia, researchers have had a hard time proving to the EPA exactly how beneficial nitrogen removal can be.

Walsh said the procedure to be implemented at Western Branch will reduce by nearly 85 percent the nitrogen left in sewage after its initial treatment, but he couldn't say what the direct benefit would be to aquatic life.

"There are certainly some R and D {research and development} aspects to what we're doing," Walsh said.

Sanitation commission officials say they will sign a contract by Monday to construct the facility and it should be completed in 1990. Schaefer said it could be six to eight years before the bay cleanup efforts begin to be visible.