The Reagan administration has denied Gov. Harry Hughes' request for federal disaster aid to about 6,000 Chesapeake Bay fishermen who lost an estimated $3 million of business because of icy conditions last month.

State officials today expressed surprise at the federal ruling, saying the icing of the bay last month was as severe as in January 1977 when the bay was declared an economic disaster area, making its fishermen eligible for federally funded unemployment benefits.

An estimated 6,000 watermen were unable to fish in the bay or its rivers and creeks for three weeks in January, when ice covered 100 percent of the Chesapeake north of the bay bridges and about 60 percent of the bay south of the bridges, Maryland officials said. Hughes had appealed to Reagan for assistance about three weeks ago.

Explaining the federal ruling, a spokesman for the Federal Emergency Management Agency said today "the severity and magnitude of the situation was not beyond the capacity of state and local governments to cope with." Spokesman Bob Blair noted that the weather has warmed considerably since Hughes' request, making it possible for fishermen to return to work.

Maryland officials said they will try to extend the state's oyster season to allow watermen to recoup some of their losses, "but what that overlooks is that these people have lost income," said Hughes' press secretary, Lou Panos. "A lot of these guys plunge right into crabbing or clamming or other kinds of fishing. They won't benefit that much from an extended oyster season."

FEMA spokesman Blair said his agency has not granted any disaster relief requests because of winter icing this year. In 1977, the agency had declared economic disaster areas in Maryland, Virginia, New York, Florida and Virginia, Blair said.