Advocates for cleaning the Chesapeake Bay are growing increasingly frustrated with the slow pace of progress, and new legal threats are emerging from groups that traditionally have pursued more conciliatory courses.

The Chesapeake Bay Foundation, which historically has worked through regulatory and legislative channels, recently established its first litigation division, and the Maryland Watermen's Association is mulling over an unprecedented class-action suit against polluters. At the same time, spinoff groups of a national organization known as the Waterkeepers Alliance have set up shop on several Chesapeake tributaries, bringing a more aggressive approach to litigation with it.

These are signs, some say, that the "Save the Bay" movement, which for more than two decades has put a friendlier face on environmentalism than many other efforts across the country, may be moving toward a more confrontational phase.

"It's only been recently that people have been questioning whether this honest, sincere, concerted effort can get us where we want to go," said Thomas W. Simpson, a University of Maryland professor who studies the bay.

The cooperative approach that some say is eroding began in the early 1980s, when several governors signed the first Chesapeake Bay Agreement.

New partnerships were created to oversee the bay's cleanup, including the Environmental Protection Agency's Chesapeake Bay Program -- billed as "America's premier watershed restoration partnership." More ambitious agreements on the bay followed in 1987 and 2000. To the environmental movement, the message from government was consistent: We're working on it.

"It was a real feeling that 10 years of concerted effort and you could turn this decline around," said Ann Pesiri Swanson, executive director of the Chesapeake Bay Commission, made up of state government officials from around the watershed.

In that atmosphere, an even-keeled environmental group grew to dominate the Chesapeake region: the Chesapeake Bay Foundation. This group -- with 116,000 members, a budget of $17.5 million and headquarters on the water just outside Annapolis -- is still the watershed's monolith.

Officials of the bay foundation, which was founded in 1967, say they've always tried to work within the mainstream. They offer educational programs to children, help restore oyster reefs and lobby state and federal officials but shy away from donating to political candidates or launching volleys of lawsuits.

This approach has made the bay foundation a holdover from an earlier era of environmentalism, said Robert J. Brulle, a professor at Drexel University in Philadelphia.

"The Chesapeake Bay Foundation is still running on the 1960s approach," Brulle said, believing "the only way to accomplish [anything] is to work within the existing system."

In some places, he said, such moderate groups have stalled and more extreme environmentalists broke off. At New York's Love Canal, for instance, residents of a neighborhood atop a chemical dump held EPA officials hostage. In the West, anti-logging activists began sitting atop old-growth trees.

The Chesapeake Bay watershed is not yet primed for that kind of radicalism, environmentalists say. But there has been growing unhappiness the past year. Last summer, former U.S. senator Charles McC. Mathias Jr. (R-Md.) marked the 30th anniversary of his proposal for a cooperative bay cleanup by calling for more accountability. "We may in fact have done some of the easier things . . . and now we have to face some of the more difficult ones," Mathias said then. "There's tough times ahead."

Anger over the lack of progress grew after the bay's "dead zone," the area of oxygen-deprived water that strangles plant and animal life, expanded to one of its highest levels ever.

This summer came the revelation that computer models used by the Chesapeake Bay Program seemed to have inflated the progress made in reducing pollution. And there is a growing sense that no matter how progress is measured, the goals set for 2010 are still far off.

For instance, to meet the 2010 goals for reducing nitrogen -- a pollutant that causes harmful algae blooms -- bay states will have to make more progress in the next five years than they made in their first 17, according to Chesapeake Bay Program data.

The disconnect between these goals and reality has curdled the enthusiasm of many supporters. "We told everybody 'Don't expect results overnight,' " said former Maryland governor Harry R. Hughes (D), who was in office when the first bay agreement was signed. "Well, it's been 20 years, and we still aren't anywhere near where we hoped to be."

Disgust with the status quo was evident when Maryland Watermen's Association President Larry Simns surveyed his membership about a potential class-action suit against polluters. There was a flood of phone calls and e-mail with the same message: "Sue the bastards," Simns said.

No suit has been filed, but Simns said the watermen are working with a D.C. lawyer who previously took on tobacco companies. Potential targets of the suit include sewage treatment plants and Pennsylvania farmers, both blamed for pollution-laden runoff that creates zones of oxygen-deprived water.

"When it comes down to watermen having to threaten to sue, it's pretty bad," Simns said. "Because watermen don't sue anybody."

The bay foundation has won some victories in court: A 1984 suit against Gwaltney of Smithfield Ltd. for illegal discharges into Virginia waterways went to the U.S. Supreme Court before the pork packer eventually paid a $284,000 fine and changed its practices.

But it has often stopped short of litigation, instead pushing for regulatory reform or legislation. This summer, though, it created a litigation arm, funded with a $1.25 million grant. The foundation has filed a petition asking the EPA to step up its enforcement against sewage plants, which could be a prelude to a huge suit. It has also filed suits against the state of Virginia and two alleged polluters there.

"Litigation is a tool that we may have to use more frequently," said Roy A. Hoagland, the foundation's executive director in Virginia.

In the past few years, citizen activists have become river keepers on the Potomac, Patuxent, Severn and South rivers, patrolling the waterways and advocating at meetings. Other changes may be brought by the offshoots of the New York-based Waterkeepers Alliance, headed by Robert F. Kennedy Jr.

One incident may foreshadow their impact: Last fall, Potomac river keeper Ed Merrifield noticed that spent ammunition from a Montgomery County skeet-shooting club was raining down into Great Seneca Creek, a Potomac tributary.

Appalled by what he said was a three-inch accumulation of lead shot on the creek bottom, Merrifield said he sent the club and their landlords at the Maryland Department of Natural Resources a notice that he might sue them under the Clean Water Act.

"Within two weeks, they locked the gates" to the shooting club, Merrifield said.

These steps toward a more confrontational environment have brought some criticism.

Officials at the EPA's Chesapeake Bay Program say there is ample evidence that the cooperative approach is still working. This week alone, Virginia announced a plan to crack down on sewage plants, and a survey of "bad water" in the bay found that it was drastically reduced last month.

Rebecca Hanmer, the program's director, said complicated lawsuits would only slow the progress. "I don't really think that litigation is the secret to cleaning up the bay," she said.

On the other side of the debate are those who feel that the recent moves have not gone far enough. Perhaps no one feels this more strongly than Howard R. Ernst, a U.S. Naval Academy professor who wrote a book, "Chesapeake Bay Blues," about the failures of the cleanup effort.

Since the book came out last year, Ernst has embarked on his own campaign of speaking engagements, decrying the "do little and delay" approach.

Ernst tells his audiences that he wants more litigation, a more politicized Bay Foundation and more aggressive punishment for polluters from the EPA.

The only way those might happen, he said, is if people get mad. "The fact that we're starting to see the conflict," he said, "means that this restoration effort is really waking up."