Already on the defensive over its domestic spying program, the Bush administration has alarmed privacy and free-speech advocates by demanding search information about millions of users of Google and other Internet companies.

Click here to read the government's motion to compel Google to turn over search data.

The moves raise questions about how far the government should be allowed to go to probe into American homes. The administration is pushing back hard, defending its surveillance as helping to protect the nation from terrorism and, to a lesser extent, shield minors from pornography.

Critics see the moves as an unwarranted expansion of presidential authority.

"Sure, the more intrusive the government becomes, the more potential crime it can solve," said Daniel J. Solove, associate professor of law at George Washington University Law School.

"But our society is founded on the fact that we don't want to give the government this broad-based power," said Solove, author of the book, "The Digital Person: Technology and Privacy in the Information Age."

The administration, seeking to revive an online pornography law blocked by the Supreme Court, has subpoenaed Google Inc. for details on what its users have been looking for through its popular search engine.

Google is fighting the Justice Department subpoena that the company has termed "unduly burdensome, vague and intended to harass." Attorney General Alberto Gonzales this week asked a federal judge in California to order Google to comply.

"We are trying to gather up information in order to help the enforcement of a federal law to ensure the protection, quite frankly, of our nation's children against pornography," Gonzales said in Washington on Friday. "We are not asking for the identity of Americans."

Yahoo Inc. and Microsoft Corp. confirmed that they had complied, at least partially, with similar subpoenas. America Online, owned by Time Warner Inc., said it provided a list of search requests already publicly available from other sources.

"You have to be alarmed at the idea that the government can come in and say, 'I want you to give me your statistical data.' This could be the first step on the way for asking for the content of the e-mails," said Shayana Kadidal, an attorney for the New York-based Center for Constitutional Rights.

The Justice Department has not asked for names or computer addresses. But the search-engine subpoenas reinforced concerns about how much personal information the government should be entitled to.

Congress is holding hearings early next month over whether President Bush overstepped his authority in ordering warrantless domestic eavesdropping by the National Security Agency as part of the post-Sept. 11, 2001, war on terror. Lawmakers, meanwhile, are also considering an administration request to extend the Patriot Act, which sharply expanded the government's ability to obtain private data on individuals.

Both the NSA eavesdropping and the demands for information on Internet consumer searches "are assertions of substantial powers that conflict with civil liberties," said I.M. Destler, a University of Maryland professor of public service who specializes in homeland security.

The White House has mounted an aggressive campaign to defend itself.

Bush will visit the NSA on Wednesday to underscore his claim that he has the constitutional authority to let intelligence officials listen in on international phone calls of Americans with suspected ties to terrorists. "The American people want us to do everything in our power to prevent attacks," White House spokesman Scott McClellan said Friday.

Gonzales and deputy national intelligence director Michael Hayden also have speeches planned for next week. And Vice President Dick Cheney on Thursday told a conservative think tank in New York that the surveillance program was an essential tool in monitoring Al Qaeda and other terrorist organizations.

A majority of people — 56 percent — said the Bush administration should be required to get a warrant before monitoring phone conversations and Internet communications between American citizens and suspected terrorists, according to an AP-Ipsos poll earlier this month.

But when people have been asked in other polls to balance their worries about terrorist threats against their worries about intrusions on privacy, fighting terror is the higher priority.

"I think people are always in favor of civil liberties in the abstract. But in specific cases, they're more free to barter those freedoms away," said Neil M. Richards, an associate law professor at Washington University in St. Louis.

In the domestic eavesdropping case, "even if it's legal, it's a really bad idea. This sort of scrutiny really does raise the specter of Big Brother," Richards said.