Maryland Gov. William Donald Schaefer's assertion this week that he intends to modify restrictions on development around the Chesapeake Bay drew strong criticism yesterday from environmentalists who said they believe he is retreating from a campaign promise.

"His comments cause me extreme concern," said Charles Fox, director of the Chesapeake Bay Project for the Environmental Policy Institute. "He's undercutting the guts of the Maryland land-use initiatives."

Schaefer said Thursday that he intends to relax parts of the state's new critical area law, which sets a limit of one house per 20 acres in some ecologically delicate areas along the bay shoreline and its tributaries..

During his gubernatorial campaign last year, Schaefer said much the same thing, but after a hail of criticism he quickly backed away from the idea and specifically said he endorsed the regulation of one house per 20 acres. He retreated from a statement that the restrictions could perhaps be relaxed in a year or two, saying he actually meant some time in the distant future -- perhaps in 50 years.

Schaefer made the latest comments during an interview at the conclusion of a regional conference in Norfolk, at which officials of three states, the District and the federal government agreed upon a major, long-term initiative to reduce by 40 percent the amount of wastes discharged into the bay.

"Naturally we were taken by surprise," said Scott Burns, a lawyer with the Chesapeake Bay Foundation. Burns said his organization would oppose Schaefer's planned changes in critical area regulations adopted in 1986, and both he and Fox said they believe the governor's plan contradicts his campaign pledge to support the critical area law.

"He's clearly reneged on a campaign promise," said Fox.

Schaefer's press office, however, disagreed. "This is no different from what he's been saying for a year," said Schaefer spokesman Bob Douglas. "He feels we need to take a look to determine if a uniform standard of one and 20 is appropriate and the best standard. It appears there are some areas where one and 20 is not enough {of a density restriction} . . . and in some areas it appears that one and 20 is more than is needed."

Douglas cited a position paper on the environment Schaefer released during the gubernatorial campaign that said he would "make adjustments and modifications when necessary" to bay conservation programs.

In the same paper, however, Schaefer specifically said he supported the density limit of one house per 20 acres in environmentally sensitive areas.

The critical area law is designed in part to protect wetlands and to preserve the natural habitats of some undeveloped shorelines. The law is strongly opposed by many Eastern Shore builders and lawmakers, who say it slows growth in the region.

"The developing business in this point in time has become a whipping boy for the cleanup of the Chesapeake Bay," said House Speaker R. Clayton Mitchell (D-Kent), a leading Eastern Shore opponent of the restrictions. Mitchell said he had talked to Schaefer on several occasions about the regulations, arguing that landowners of small parcels would be better equipped to battle shore erosion than owners of 20-acre parcels.

Still, said Mitchell, a revision by the General Assembly of the hard-fought critical area law "is going to be a hard one to sell. I think we're going to have to prove our case."