WASHINGTON — A total of 2 million households in five cities will have a surprise visit from their letter carrier this summer, and the carriers won't be delivering mail.

Escorted by a police officer, they will deposit up to two bottles of emergency doxycyclene in each mailbox, first responders to a fictional anthrax or other bioterrorist attack.

The pill bottles won't actually contain real drugs. But everything else about the delivery will look real, a scenario designed to prepare local officials for a biological terror attack with a quick strike delivered by the U.S. Postal Service.

The mail carriers, all volunteers, are the lynchpin of a pilot program that launched with a dry run May 6 in Minneapolis/St. Paul and will continue until the end of September in Louisville, San Diego, Boston and Philadelphia. With a $10 million budget approved by Congress, the postal service is teaming up with the Department of Health and Human Services, state and local health officials and law enforcement agencies to devise a program that would deliver doses of antibiotics to thousands of households in each city within hours of an attack.

 The tests follow an executive order President Obama issued three years ago to create a model where postal workers would deliver medication during a widespread biological emergency. The idea is to keep people from panicking as they head to medicine distribution centers and to reduce lines.

 "Our idea is to get the medicine out there as quickly as we can, so we can help health officials set up other dispensing locations" like hospitals, schools and doctors' offices, said Jude Plessas, who manages the pilot program for the postal service. "We're using an infrastructure that already exists to help with the local response."

  Plessas and DeLaine Black, who is in charge of the program for HHS, briefed the Postal Regulatory Commission, which oversees postal service policy, on the pilot program on Tuesday.

  Commission Chairman Ruth Goldway praised the postal service for preparing its workers to provide a vital public health service "that goes beyond mail delivery and that isn't recognized," especially as the agency struggles with multi-billion-dollar deficits.

  "Here we have people who are familiar with every street within a neighborhood who are participating in this exercise," she said.

  Under the terms of the National Letter Carriers Association's contract with the postal service, mail carriers can't be forced to be first responders but can volunteer, officials said. Hundreds of mail carriers have raised their hands and been trained.

  A week before the dry run in the Twin Cities, the Minnesota Department of Health sent fliers to 33,000 residential addresses in five zip codes, officials said. On the day of the test, a Sunday, about 300 mail carriers and their police escorts left empty pill bottles in mailboxes on their routes.

 Plessas said the "team concept" of a letter carrier and police officer is designed to speed up delivery of medicine in a real disaster. Residents would be likely to have questions the officer could answer while the carrier delivered the antibiotics, for example.

  Officials said the mail carriers could be deployed within hours of an anthrax attack, as soon as the Centers for Disease Control and Prevention gave the order to local health officials to release medicine.

  Another two cities are under consideration for pilots, but without new funding, the program cannot expand, officials said.

  An anthrax attack in 2001, soon after the terrorist attacks of Sept. 11, killed five people and left 17 others ill. The mail service was crippled after anthrax-laden letters were sent to congressional offices, media outlets and others.

  In 2008, federal prosecutors identified scientist Bruce Ivins, who worked at the government's biodefense labs at Fort Detrick, Md., as the suspect. Ivins had killed himself days before. The FBI closed its investigation in 2010. But a year later, a federal panel concluded that the FBI had overstated the strength of genetic evidence linking the anthrax to the supply kept by Ivins.

After the 2001 attacks, more than 10,000 people took antibiotics, including doxycycline, Cipro and other drugs, to prevent infection.