With an eye toward cleaning up the Chesapeake Bay, William D. Ruckelshaus went for a cruise on it today, along with the governors of Maryland and Virginia, the lieutenant governor of Pennsylvania and U.S. senators from the three states.

Ruckelshaus, administrator of the U.S. Environmental Protection Agency, pronounced it a "delightful trip" during which all were "in agreement the bay is a very important national treasure and this may well be a model of state-federal cooperation."

He was unwilling to talk dollars, however. "We haven't yet discussed additional funding," he said. "Obviously, it's going to cost additional money if the problems are gonna be solved."

Ruckelshaus joined the others on one of seven ships assembled for an event intended to demonstrate a federal-state commitment to clean up the nation's largest estuary and--in particular--to win the Reagan administration's support. Altogether, more than 100 officials, aides, journalists and crew participated in the convoy across the bay and back.

It was billed as a major meeting on the water, taking place in the wake of a five-year, $27 million EPA study of the bay, and leading to a December "summit meeting" of decision-makers from the three states through which the estuary and its tributaries pass.

"It's a little premature to suggest how much money any level of government should put in," Ruckelshaus told reporters at dockside. But the cruise showed that "we're in this together," he said. "I was positive before, and I'm even more positive now."

The bay study concluded that the 10,000-year-old estuary is suffering from too many toxic substances and nutrients that reduce the water quality and oxyen content needed to sustain a wide variety of aquatic life.

Since the preliminary results were released several months ago, officials and scientists have been talking about the implications, both financial and political. Maryland Gov. Harry R. Hughes, host of today's outing, has made the bay's salvation a major goal.

"We're beyond the study phase," said William Eichbaum, environmental chief of the Maryland health department. "That's what's important about this."

Hughes was joined on the Aurora, a state-owned yacht, by Ruckelshaus and by Gov. Charles S. Robb of Virginia, Sen. John W. Warner (R-Va.), Sens. Charles McC. Mathias Jr. (R) and Paul S. Sarbanes (D) of Maryland, Sen. Arlen Specter (R-Pa.) and Pennsylvania Lt. Gov. William Worthington Scranton.

The vessels paused below the bay bridge to observe such planned activities as clam dredging, students' taking water samples, crabbers' checking and replacing their wire-mesh pots, and oystermen's tonging out of season--a reprieve for today only.

Then the officials donned oilskins and gumboots and hosed oyster shells from a barge onto Hackett's Bar, a shoal area where the bivalves have long been harvested. They meant to learn firsthand about Maryland's program to move millions of old shells each year from the unproductive upper bay farther south.

Ruckelshaus said he was pleased that the proposed new federal budget contains $4.2 million more for bay research, but declined to commit himself to legislation that would authorize much more for water quality management.

"The administration, in the form of me standing here now, is very interested in the bay and will continue to be interested in the future," he said.