Amid concerns about its effectiveness and multibillion-dollar cost, the Department of Homeland Security has canceled plans to install an automated technology that was meant to speed the 24-hour operations of BioWatch, the national system for detecting a biological attack.

The cancellation of the “Generation 3” acquisition was made Thursday at the direction of Homeland Security Secretary Jeh Johnson, according to a memorandum circulated by Michael V. Walter, the BioWatch program manager.

Homeland Security officials earlier had told companies interested in supplying the technology that it would spend $3.1 billion for it during the first five years of operation.

To date, the overall BioWatch program has cost taxpayers more than $1.1 billion.

Walter said in his memo that the department “remains committed to the BioWatch program and the importance of improving our early warning and detection technologies.”

A Homeland Security spokesman, S.Y. Lee, said the cancellation reflected a commitment to “cost-effective acquisition without compromising our security.”

Johnson’s decision to cancel the technology marks a reversal of policy.

For the better part of a decade, officials from both the Obama and George W. Bush administrations have told Congress that Generation 3 — described as a “lab in a box” that could sift air for viruses, germs and other biological threats and relay findings electronically — was worth the investment.

In February 2007, Jay M. Cohen, a Homeland Security undersecretary, told a House committee that Generation 3 would be “four times cheaper to operate” than the existing BioWatch system, which relies more on manual operations.

In March 2012, Dr. Alexander Garza, the department’s chief medical officer, told a House subcommittee that Generation 3 would be “imperative to saving thousands of lives.”

Behind the scenes, doubts festered.

Articles published by the Los Angeles Times in 2012 and 2013 reported numerous deficiencies with BioWatch. They also pointed out shortcomings with the new technology’s durability and reliability.

For instance, automated prototypes installed in the New York subway system in 2007 and 2008 produced multiple false readings, prompting a city police official to order their removal.

In 2011, field testing in Chicago of a second prototype found that it could not operate independently, without manual servicing, for more than a week at a time.

Several congressional panels held hearings, pressing Homeland Security officials for answers. Last August, a bipartisan group of House members asked the U.S. Government Accountability Office to examine the performance of the existing BioWatch system and to assess to what extent the proposed new technology would “provide additional benefits.”

The GAO review remains ongoing. A September 2012 GAO report estimated that annual costs to operate Generation 3 would be “about four times more” than for the existing BioWatch system.

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