The Bush administration has announced plans to reopen the most sweeping — and most controversial — clean water rule developed during the Clinton administration.

In July, EPA Administrator Christie Todd Whitman announced the agency would put on hold the implementation of new rules guiding the development of water cleanup plans, know as Total Maximum Daily Loads, which were approved in 2000.

The EPA filed a motion in the District of Columbia Circuit Court asking it to halt action on numerous lawsuits challenging the rule for 18 months while the agency reviews and revises the rule.

“In order to ensure that this nation’s bodies of water are cleaned up, we need an effective national program that involves the active participation and support of all levels of government and local communities,” Whitman said. “Unfortunately, many have said the rule designed to implement the TMDL program falls short of achieving the goals.”

The new rule was highly controversial because it would have stepped up efforts to control runoff from farms and other land uses which are the primary source of pollution to most “impaired” waterbodies.

Whitman’s announcement was praised by critics of the rule, including many states who said it was too difficult and costly to implement, and by farming groups and others who said the EPA had overstepped its authority in addressing runoff.

But environmental groups worry that the EPA will cripple the TMDL program, which they see as a critical tool for cleaning up waterways that remain polluted nearly three decades after the Clean Water Act was passed.

The issue could be important to the Chesapeake because the TMDL program is the regulatory backup if the Bay Program efforts fail to clean up the Chesapeake by 2010. Under a court-approved consent agreement, the Bay will need a TMDL unless it meets water quality standards by 2011.

At the core of the issue is how Section 303(d) of the Clean Water Act, which sets up the TMDL program, is interpreted and implemented.

Historically, pollution efforts were focused on forcing pollution reductions from “point source” dischargers, such as industries or wastewater treatment plants. Usually, that was done by requiring the use of specific technologies — or their equivalent — which would control certain types of pollutants.

Section 303(d) the Clean Water Act requires that after those programs are implemented, states must identify “impaired” waterbodies — those that fail to meet water quality standards — and develop TMDLs for them.

A TMDL is essentially a “pollution budget” for a waterway. It is an estimate of the maximum amount of a pollutant that a body of water can receive and still meet its water quality standards with a margin of safety. Once the maximum load is calculated, it is allocated among different pollution sources.

Although on the books for nearly 30 years, the TMDL requirement was largely overlooked until environmental groups began suing the EPA in the past decade to force the issue.

But rules governing TMDL development were considered vague by many. For example, it was unclear whether the cleanup plans had to be implemented once written. In part, that’s because many of the polluted waterways are impaired by runoff pollution, for which there are fewer enforceable regulations.

The new rules required states to develop implementation programs as part of a TMDL, and to provide “reasonable assurance” that those plans would be carried out. For example, if action was needed to control runoff, the plan would have to show that regulations exist to achieve the cleanup goal, or that voluntary programs were adequately funded to do the job.

If states failed to write and implement TMDLs, the new rules said the EPA would step in and write the plans, and would assume responsibility for issuing permits in the impaired waterbody.

When approved, then-EPA Administrator Carol Browner called the rules “the single most important action in a generation for cleaning up America’s polluted rivers, lakes and shorelines.”

But the rules have never taken effect because Congress last year blocked their implementation until this October.

Many critics questioned whether there was sufficient science to even conduct a TMDL program.

But a recent National Research Council report concluded that “the state of the science is sufficient” to develop TMDLs in most situations. It generally applauded the TMDL approach to address the health of waterbodies as a whole, rather than focusing only on chemical discharges, as in the past.

At the same time, the report said that water quality monitoring was often so poor that it is difficult to be sure that the all of the 20,000 water bodies on the TMDL list are actually impaired. It suggested that the EPA should create a “preliminary” list of waters that need more data to be certain they require TMDLs.

The panel also suggested that parts of the program be strengthened. For example, it said TMDLs should be developed not only for waterways impaired by chemical pollutants, but also for those that have lost habitat because of channelization, alterations in water flow and changes in water temperature.

Farm groups were among the strongest critics of the rule, and they contend that that the federal government cannot regulate runoff because it has no authority over land uses, such as farming, which generates such “nonpoint” pollution.

“It was unfortunate Farm Bureau and others had to challenge in court the EPA’s authority under the Clean Water Act to include nonpoint sources in the TMDL regulatory water program,” said American Farm Bureau Federation President Bob Stallman. “However, we agree with the 18-month stay of the litigation and look forward to working with the EPA to revise the regulations.”

But environmentalists — and court rulings — contend that the TMDL program was intended to cover runoff, noting that the act calls for writing the cleanup plans after controls have been installed at point sources.

“The law doesn’t make any sense if you don’t think of it as including nonpoint sources,” said Joan Mulhern, of the group Earthjustice, which has been representing many environmental groups in TMDL litigation.

She and others believe the EPA will propose eliminating the requirement that the agency must approve enforceable implementation plans as part of a TMDL, something that one former agency official said would sharply reduce the effectiveness of nonpoint source controls.

Other changes could make it more difficult for citizens to get waters put on the TMDL list, and make it easier to take waters off the list. For example, some people have suggested that waterways could be taken off the impaired waters list based on computer models saying that a TMDL would clean up the waterbody, rather than actual monitoring data.

“The Chesapeake Bay could come off the list of impaired waters based on a model that says you should be meeting water quality standards as opposed to actual data that you are,” said a former EPA official.

Right now, the EPA is required to write TMDLs if the states fail to do so. Another possible change would be to make that requirement discretionary on the part of the EPA.

“If they do that, it is another blow at the heart of the program,” Mulhern said. “The Clean Water Act is premised on the notion that all of our nation’s waters should be clean, that there is no place where citizens do not deserve clean water. The whole reason to have a national program and a strong federal role is to ensure that there is not a race to the bottom.”

While the EPA recommends changes in the new rule, TMDLs will continue to be written under the old rules.

A recent EPA estimate said it costs about $52,000 to develop an average TMDL, and that implementing the cleanup plans nationwide will cost between $900 million and $4.3 billion a year.