BALTIMORE, JULY 28 -- A newly inaugurated ferry service across the Chesapeake Bay was closed down this weekend when its only vessel struck an underwater object, damaging the hull and prompting cancellation of further trips until repairs are completed, a ferry service official said today.

Jean Stone, sales manager for the Chesapeake Flyer ferry service, said the high-speed, 105-passenger catamaran Chesapeake Flyer hit an unidentified object late Friday or early Saturday in Baltimore as it was finishing its last trip for the day from Rock Hall on the bay's eastern shore.

"The passengers were able to disembark and there was no threat of sinking," she said.

The $1 million twin-hull craft, however, had to be taken out of service for repairs, Stone said, canceling scheduled trips today and Sunday. The ferry does not run on Mondays -- a regular maintenance day -- "and it is our hope to have her operational again by Tuesday," she said.

The ferry service -- the first to offer regular cross-bay transportation in almost 40 years -- officially started Wednesday amid a splash of publicity with six daily runs between Baltimore's Inner Harbor, Rock Hall in Kent County, and Annapolis.

The Flyer, styled after similar ferry boats in San Francisco, Boston and Chicago, travels up to 30 miles per hour and makes the run from Baltimore to Rock Hall in about 75 minutes. The round-trip passenger fare is $19.25. The ferry carries no cars.

Promoted as a tourist attraction, backers hope to parlay it into a year-round, water-borne commuter service in 1991 for Eastern Shore residents who work in Baltimore.

Ferry service President Ron Calloway, who could not be reached today, has said that he hopes to spur commuter business with construction of a new residential development he and other investors have started in Rock Hall. Called Rock Hall Landing, the $40 million, 52-acre complex will include town houses, detached homes and condominiums adjacent to a marina where the Chesapeake Flyer docks. If all goes as planned, Calloway envisions reduced commuter fares for the round-trip journey.

Few Baltimore commuters live in Rock Hall now. But Calloway says the twin attractions of cheaper housing on the Eastern Shore and faster commuter time on the ferry (it takes two hours by car over the Chesapeake Bay Bridge) should draw buyers.

At the moment, Calloway has no second boat to replace the Chesapeake Flyer. Cancellation of the weekend trips "represents a very large chunk of revenue" for the new enterprise, said sales manager Stone.