This year could be decisive for the Chesapeake Bay. It is the year the 1983 bay agreement must be renewed, and that agreement will literally determine the fate of the bay.

Despite the progress to date, the bay remains embattled. Each day agricultural and urban runoff, along with pollution from industrial facilities and sewage-treatment plants, assaults it. Excessive amounts of nutrients and toxic chemicals continue to threaten its priceless resources.

As a result, recreational activities have been curtailed and strains increased on the watermen who depend on the bay for their livelihood. We need to act decisively and promptly to reverse the decline and begin the process of upgrading the bay's water quality.

The basis for a general strategy will be a special report that the state/federal Chesapeake Bay Program will issue this September. It will be detailed analysis of the bay's conditions and will contain program alternatives to restore the bay to health.

The preliminary indications emerging from the report present persuasive evidence that significant steps to reduce the levels of nutrients and toxics in the bay are essential. While we naturally associate nutrients with robust health, in the case of the bay there can be too much of a good thing. In its complex ecosystem, an oversupply of nutrients leads to a decline in oxygen necessary for fish and other water life. The reason is that nutrients contribute to an excessive growth of microscopic plants, particularly algae, which deprives fin fish and shellfish of needed oxygen. As a result, there is a decrease in the bay's bounty.

In order to confront this problem, we must first scientifically establish the amount of nutrients entering the Chesapeake Bay. Then, of course, we must work to reduce the excessive amounts. Although we cannot now define with precision their contribution to pollution in the bay, tentative estimates suggest that a reduction in nutrient levels somewhere in the neighborhood of 40 percent will be required for marked improvement. This goal will not be achieved overnight, but a timetable and targets for reducing the nutrients year by year are indispensable to the bay's revitalization.

Toxic compounds also have a direct effect on the life of the bay. In large amounts these compounds can be lethal to fish; small amounts can reduce reproduction rates and cause lesions or fin erosion. The variety of toxics is stunning. They include metals such as lead and copper, organic chemicals such as PCBs and Kepone and chemicals such as chlorine. Industrial facilities and sewage treatment plants discharge a variety of toxics, and control of these compounds must begin at the source.

A number of steps can be taken immediately. First, we need to continue to upgrade enforcement of the state's Pollution Discharge Elimination System. The Clean Water Act gives the states authority to regulate discharges by means of permits. This permit process needs to be more systematic. Second, we must move ahead with Superfund cleanup. The cleanup of toxic waste sites will reduce runoff into our waterways and contribute measurably to a healthier bay.

These cleanup activities are some of the goals that must be included in any new bay agreement. They are fundamental to restoration of the bay, our nation's most productive and precious estuary.

Paul Trible is a Republican senator from Virginia.