The state Agriculture Department said yesterday it has canceled all poultry exhibitions indefinitely after preliminary tests indicated the presence of avian influenza in a flock of chickens in Lancaster County.

Antibodies for the virus were detected in an egg from a Mount Joy farm as part of routine surveillance, but officials said it was not immediately clear whether the virus was alive or only an indication of past exposure.

"The flock is currently exhibiting no signs of clinical disease or increased mortality," said Agriculture Secretary Dennis C. Wolff. "Additional samples are being tested to determine whether the virus remains present. We are aggressively monitoring the situation and taking all necessary precautions to isolate the disease."

The announcement came amid heightened concern over the avian flu because of recent outbreaks on two farms in neighboring Delaware, which led to the destruction of 80,000 birds, and the recent discovery of the same strain of avian flu at several live chicken markets in northern New Jersey.

The strain found in Delaware and New Jersey is not the one that has spread to humans in Asia, killing at least 18 people. It is not harmful to humans.