Part of the hospital at Andrews Air Force Base was quarantined for more than two hours last night after a patient arrived with symptoms resembling smallpox, Air Force officials said.

The patient, who came to the Malcolm Grow Medical Center emergency room, was eventually found to have a severe case of chickenpox after a specialist from Walter Reed Army Medical Center was sent to the hospital, Andrews officials said.

Symptoms of chickenpox and smallpox can be similar, and a spokeswoman for the base, which is home to Air Force One, said the incident came at a time of heightened concern about possible terrorist attacks using infectious agents.

The hospital said the patient and the three medical personnel she came in contact with were isolated as a precaution, and the emergency room was closed from 6 to 8:15 p.m. Base personnel requiring treatment were taken elsewhere by the Prince George's County fire department.

According to a statement from the base's public affairs office, the patient, a member of a military family, came in about 6 p.m. complaining of a "low-grade temperature" and difficulty breathing. The patient, who was not identified, also complained of the sudden development of a rash.

Andrews said medical center personnel took "all necessary precautions since her symptoms were very similar to those of smallpox."

Smallpox, a deadly and highly contagious disease, was believed to have been eradicated in the late 1970s, but supplies of the virus that causes it still exist.

Its early symptoms include high fever and a rash. Smallpox and chickenpox both produce red blisters on the body, but they differ in size and location and in the timing of their appearance.

Staff writer Steve Vogel contributed to this report.