While oozing bipartisan collegiality in public, two Maryland congressmen are locked in what one describes as "a very complicated political chess game" that both lawmakers agree will shape the future of the Chesapeake Bay.

For months, Rep. Steny H. Hoyer, a Democrat from Prince George's County, and Rep. Wayne T. Gilchrest, a Republican who represents Anne Arundel County and the Eastern Shore, have been maneuvering behind the scenes over the Maryland Port Administration's controversial plan to dump 18 million cubic yards of dredge spoils at a spot known as Site 104, near the Chesapeake Bay Bridge. The state says the dredging is necessary to keep clear the 50-foot deep approach of the Baltimore channel required by the largest modern cargo ships.

Gilchrest, a maverick Republican with an environmentalist bent, is seeking to kill the proposal, saying it is a threat to the health of the bay. Hoyer, the dean of the state's congressional delegation and firmly allied with Gov. Parris N. Glendening (D), is seeking to protect the Site 104 plan, saying it is ecologically sound and essential to the health of the Maryland economy.

As debate over the merits of Site 104 has intensified this year, the issue, in effect, has been federalized. Hoyer and Gilchrest have emerged as point men in a classic struggle over the best way to balance economic and environmental considerations for the nation's largest estuary.

On Sept. 27, when a House-Senate committee approved the Energy and Water appropriations bill, the latest phase of what Gilchrest called a "complicated political chess game with a very sophisticated opponent" ended with both men claiming the advantage and vowing to fight on.

"I'm ecstatic," Gilchrest said, after the conference report was approved, citing language that obligates the U.S. Army Corps of Engineers "to thoroughly analyze and review all practicable alternatives" to Site 104.

Hoyer, too, said he was pleased with the conference report but for different reasons. In a statement issued by his office, he emphasized that conferees had funded four dredging projects in the Baltimore Harbor, which he said would help keep the state's waterways "healthy and navigable."

For Hoyer and his allies in the state government, the bay is a pillar of the state's economic infrastructure. They claim that 126,000 jobs statewide are directly or indirectly dependent on goods coming and going through Baltimore Harbor, creating $1.8 billion in wages and generating $290 million in state, county and local taxes.

State officials are frustrated by the environmental opposition, especially from the U.S. Fish and Wildlife Service. They note the state task force that recommended Site 104 be used included environmental groups and federal agencies that signed a memorandum of understanding agreeing to rely on disposal in the bay.

They also note that the state currently dumps dredge spoils in the Chesapeake's waters near Poole's Island in the northern part of the bay without environmental damage or protest.

This is the case that Hoyer has carried to Capitol Hill. In May, he arranged for Glendening to meet with Rep. Ron Packard (R-Calif.), who chairs the House Energy and Water subcommittee. According to a Packard aide, the Maryland governor stressed the importance of dredging to the Maryland economy.

By then Gilchrest was championing the alternative view of environmentalists and citizen activists: that the health of the bay ecosystem is the key to its economic, recreational and ecological value. They cite scientists who say dumping at Site 104 would release 1.2 million pounds of nitrogen into the waters near the Bay Bridge.

This could cause algae blooms that would block sunlight from reaching ecologically important aquatic grasses and threaten short-nose sturgeon, crabs and oysters, they said.

In June, Gilchrest began publicizing the views of some officials with the U.S. Fish and Wildlife Service and the National Marine Fisheries Service, who believed the Army Corps of Engineers had not adequately analyzed the impact of dumping on water quality and aquatic life. Within weeks, the Corps decided to withdraw its draft environmental impact statement on Site 104 and reexamine the issues involved.

Gilchrest then persuaded the House Energy and Water subcommittee to adopt language directing that Site 104 not be used until all other alternatives had been exhausted.

Hoyer privately tried to get Packard, the committee chairman, to drop the language, according to sources close to the issue. When that failed, he told the committee that he had "concerns" about Gilchrest's language and that the Site 104 issue needed "broader discussion."

In the fall, both Hoyer and Gilchrest appealed to Packard, a member of the House-Senate conference committee preparing the final version of the appropriations bill, to adopt their view of the Site 104 controversy. Seeking to be "even-handed" in the words of an aide, Packard adopted some of Gilchrest's restrictions on the Army Corps while agreeing with Hoyer to delete its strongest language.

A spokesman for Hoyer pointed out that the conference committee report omitted one Gilchrest-authored sentence which would have "directed" the Corps to "use all other alternatives" before disposing of dredge material at Site 104.

"That language that was cut would have made it harder to move forward with Site 104," said Debra DeShong, Hoyer's press secretary.

Gilchrest said the omission was not important.

"The conference report underscores that the Congress agrees with the Environmental Protection Agency and the Fish and Wildlife Service that there is no justification for Site 104," Gilchrest said.

"This adds to our momentum," he said.

The next phase of the struggle comes this winter, as the Corps of Engineers prepares a new draft environmental impact statement about Site 104. That statement, a Corps spokesman said, is scheduled to be finished in December.

CAPTION: STENY HOYER

CAPTION: WAYNE GILCHREST