The Bush administration said yesterday that it plans to start using the nation's most advanced spy technology for domestic purposes soon, rebuffing challenges by House Democrats over the idea's legal authority. Homeland Security Secretary Michael Chertoff said his department will activate his department's new domestic satellite surveillance office in stages, starting as soon as possible. Sophisticated overhead sensor data will be used for law enforcement once privacy and civil rights concerns are resolved, he said. His statements marked a fresh determination to operate the department's new National Applications Office. But Congress delayed launch of the new office last October. Critics cited its potential to expand the role of military assets in domestic law enforcement, to turn new or as-yet-undeveloped technologies against Americans without adequate public debate, and to divert the existing civilian and scientific focus of some satellite work to security uses. Democrats say Chertoff has not spelled out what federal laws govern the NAO, whose funding and size are classified. Congress barred Homeland Security from funding the office until its investigators could review the office's operating procedures and safeguards. The department submitted answers on Thursday, but some lawmakers promptly said the response was inadequate. [Rep. Bennie G. Thompson (D-Miss.), chairman of the House Homeland Security Committee] said, We still don't know whether the NAO will pass constitutional muster since no legal framework has been provided."