MANY boaters on the Bay will soon be required to pump more than just gasoline.

Legislation approved by the Maryland General Assembly will require all marinas with more than 50 slips, as well as all new or expanding marinas with 10 slips or more, to install sewage pump-out facilities. In addition, the 12,000 boats equipped with holding tanks that are registered in Maryland waters will be required to use those facilities to pump out their wastes.

The legislation, sponsored by Maryland members of the Chesapeake Bay Commission, will be phased in over the next three years. By 1997, the law will ensure that at least 200 additional pump-outs are in place, tripling the number now available in the state. After that time, boaters whose vessels have holding tanks could face a fine of up to $2,000 if they dump their wastes in the water.

Thanks to a recent federal grant, marina owners will not have to pay to install the pump-outs. Virginia and Pennsylvania also received federal grants recently to aid with pump-out installation [see related story]. While not a major source of nutrient pollution Baywide, waste discharges from boats can create local water quality problems.

Efforts to control boat pollution have been hindered by the dearth of pump-outs around the Bay. In Virginia and Maryland combined, working pump-outs are available at fewer than one-quarter of the marinas. As a result, many boaters have abandoned the whole pump-out concept, and some marinas with pump-outs have complained of a lack of demand for the facilities among boaters.

The popularity of pump-outs appears to be linked to marina staff who advocate their use. This illustrates the importance of education in promoting pump-outs and the role of the marina manager in changing boaters' behavior. "We installed our pump-out in 1990 and we've had no problems," said Joe Pomerantz, general manager of the Piney Narrows Yacht Haven. Because of the importance of a clean Bay and a clean marina, he offers his pump-out free of charge to lure boaters seeking gasoline and other services. It takes about one minute to pump a 15-gallon holding tank - less time than it takes to gas up a large power boat - and the suction fitting is clean and easy to operate.

To some, such as Jonathan Jones of the Haven Harbor Marina, pump-out use is a stewardship issue. Haven Harbor's pump-out, the first installed in Rock Hall, has been operating reliably since 1986. At that time, Jones believed pumping waste to be important enough to offer a $5 gift certificate to the marina supply store for boaters who used it. Although the certificates have been discontinued, the service is still free and the staff helps to educate boaters about pump-outs and other environmental boating services that the marina offers free or at cost. "People can change," Jones said, "but they need some help along the way."

In locations such as Baltimore, Annapolis, or Washington - where the supply of pump-outs is woefully inadequate - boaters have long had little choice but to dump overboard. Accustomed to the lack of pump-outs available in their home ports, they traverse the Bay with their "Y"-valves cocked open, oblivious to pump-out stations lining the shores in many popular boating destinations, such as Rock Hall, Kent Narrows, and the Chester River.

Maryland's new law alleviates this problem by making pump-outs more widely available and easily accessible. Much as past campaigns to reduce littering relied on the placement of trash cans on street corners, proponents believe a campaign to reduce boat pollution will be successful only if there is a "critical mass" of pump-outs conveniently distributed throughout the Bay. This will require persistent, coordinated actions by all the Bay jurisdictions.

The effort to promote pump-outs will have added teeth stemming from approval of a bill introduced by Delegate Michael H. Weir. The measure wrote into Maryland law Coast Guard regulations that require boat owners with holding tanks to keep their "Y"--valves - which can direct wastes into the holding tank or into open water - in the closed position when within three miles of Maryland's coast or face a fine. This bill, which takes effect in 1997, was considered a natural complement to the pump-out law and was seen by those in the marina business as essential to creating a demand for the newly installed facilities.

Still, many aspects of pump-outs vex boat owners and marina operators alike. Some manufacturers install substandard systems which result in leaks and odors. There are inconsistent standards for hose fittings and adapters as well, which can sometimes make pumping a messy affair. Marina owners worry about odors, spills, and boat traffic obstructing other marina services.

But these problems tend to be the exception rather than the rule. There are holding tanks that work flawlessly, pump-outs that are easy to use and are nearly maintenance-free, and perhaps most importantly, boaters and marina owners alike who favor the idea. One Annapolis dockmaster reported the dismay of boaters traveling Maryland's Intercostal Waterway from Great Lake locations like Michigan - where "Y"--valves are illegal - at being told that no pump-out facility was available.

The divergence in attitudes and practices from one region to another highlights the crux of this issue: Boat pollution is no longer a technological or logistic problem, but rather a behavioral one. As pump-outs become more abundant than excuses, officials hope the concept will begin to take hold among Bay boaters.