WASHINGTON - Maryland's congressional delegation, alarmed by the weekend appearance of avian influenza on the lower Eastern Shore, were reassured by a U.S. Department of Agriculture veterinarian yesterday that local officials and the industry are acting aggressively to contain the economically dangerous disease.

Andrea M. Morgan, associate deputy administrator for veterinary services with the USDA's Animal and Plant Health Inspection Service, also said the federal agency is developing a surveillance program to help stamp out cases of the contagious flu in live-bird markets. The USDA believes the markets, particularly numerous in New York and New Jersey, circulate the virus from one region to another.

From a prevention standpoint, "it's most important that we address the live-bird markets," Morgan said.

"We have seen that those markets can be a threat to our industries," added Bill Satterfield, executive director of the trade group Delmarva Poultry Industry Inc.

More than 325,000 chickens near Pocomoke City in Worcester County have been killed since the virus - the same strain found on two farms in Delaware last month - was detected on a commercial farm Saturday. Maryland agricultural officials say 40,000 more birds that tested clean will be destroyed this week because they're in houses owned by the same farmer.

This is the first case of the flu on a commercial chicken farm in Maryland and the third ever on the tri-state Delmarva peninsula, where the poultry industry is a major employer.

Poultry generated $440 million in Maryland alone in 2002, and most of the grain in the state is grown to feed chickens.

"Maryland's poultry industry is the cornerstone of the state's agricultural economy," Sen. Paul S. Sarbanes said during the briefing yesterday.

More than 1,000 farms on the peninsula have tested negative for the disease since it popped up in the Delaware counties of Kent and Sussex, part of a containment effort that includes quarantining and disinfecting.

As it had earlier promised, Maryland lifted restrictions yesterday on the movement of poultry and poultry manure north and east of U.S. 50 but said restrictions remain in place south of the highway. Delaware also lifted its restrictions yesterday on spreading poultry litter and cleaning poultry houses.

Unlike the deadly Asian strain, the avian flu found in Maryland and Delaware is not known to harm humans. But it can kill birds, and officials want to stamp it out to keep it from mutating or otherwise threatening the chicken industry.

In the past month, more than three dozen countries have banned poultry from certain U.S. states or all of the United States. Cases of avian flu have also been found recently in Pennsylvania, New Jersey and Texas.

Morgan said the U.S. government is trying to convince countries to ban only poultry from Texas because the strain found there was highly pathogenic.

Satterfield said government and industry officials destroyed some flocks without the flu to convince foreign trading partners that the outbreak will not become an epidemic.