In response to initial tests showing anthrax contamination in two Defense Department mailrooms, the U.S. Postal Service has shuttered the facility that processes government mail, temporarily halting delivery to all D.C.-area federal agencies, including Capitol Hill.

Congressional officials said Tuesday, however, that mail delivery to House and Senate offices will remain on schedule, and they sought to assure House and Senate employees that the parcels are safe.

“For the next two days, mail already delivered by the USPS and cleared by the vigorous testing methods applied by the House’s mail screening process will be delivered to House offices,” House Chief Administrative Officer Jay Eagen wrote to lawmakers and their staffs today.

An aide to Senate Sergeant-at-Arms Bill Pickle made a similar statement: “The Senate has a thorough and sophisticated mail processing system in place. Any mail delays or suspension would be as a result of the U.S. Postal Service authorities doing so until final testing is completed at the Pentagon.”

The delivery of newspapers, packages from carriers other than the post office, “Dear Colleague” letters and other inside mail will likewise continue on schedule, Eagen wrote.

House officials noted, however, that if mail facilities remain closed, delivery to Capitol Hill could be affected beginning Thursday, along with other government offices that receive mail from the USPS’ V Street facility in Northeast Washington.

The closure followed the Defense Department’s decision to shut two mail processing centers — a Pentagon-based facility and a Fairfax County site — Monday evening, after hazardous materials sensors detected anthrax in the mail.

Although mail addressed to Congress is irradiated by the USPS and tested for a variety of substances, both the House and Senate utilize extensive mail screening procedures at separate off-site facilities before delivering mail to the offices. This causes a short delay in delivery to Capitol Hill.

A senior House aide added that in addition to mail received Friday and Monday, the chamber’s off-site mail processing plant has also been tested for anthrax contamination.

“All tests to date on that mail — and within the facility — have returned as negative,” the aide said. “In consultation with our biological experts, the House has determined that the mail we have is safe and, after a slight delay this morning, normal mail deliveries to the campus will occur today.”

The Congressional off-site facilities, which opened in February 2004, came in response to the chemical and biological attacks that had shut down Capitol Hill twice in a three-year period.

After anthrax-laced letters were delivered to the office of then-Majority Leader Tom Daschle (D-S.D.) in October 2001, the Hart Senate Office Building remained shuttered for three months.

Similarly, the discovery of the toxin ricin in the personal office of Senate Majority Leader Bill Frist’s (R-Tenn.) in February 2004 prompted the temporary closure of the Senate’s three office buildings and brought mail delivery on Capitol Hill to a standstill.