Michael Chertoff, the homeland security secretary, waived several environmental laws yesterday to continue building a border fence through a national conservation area in Arizona, bypassing a federal court ruling that had suspended the fence construction.

Citing “unacceptable risks to our nation’s security” if the fence along the border with Mexico was further delayed, Mr. Chertoff invoked waiver authority granted him under a 2005 bill that mandated construction of the fence.

He ordered work to continue on 6.9 miles of fence along the border through the San Pedro Riparian National Conservation Area in Cochise County in southeastern Arizona.

In a ruling on Oct. 10, Judge Ellen Segal Huvelle of the federal court for the District of Columbia held up construction of the fence, finding that the government had failed to carry out the required environmental assessment. The decision came in a suit brought by the Sierra Club and Defenders of Wildlife.