In order to rescue a constitutionally suspect federal law, the U.S. Justice Department is doing what law-enforcement agencies have traditionally done in times of crisis — forming a posse. But one prospective member, the Internet search giant Google, refuses to be deputized.

High-tech Google’s stand would resonate with the nation’s 18th-century founders. They distrusted centralized power, and they would have disapproved of federal officials’ attempt to turn private-sector institutions into government agents.

Justice Department lawyers, desperate to revive the 1998 Child Online Protection Act, or COPA, have subpoenaed Google, Microsoft, Yahoo and America Online for information about search-engine activity. While the latter three reportedly have complied, at least in part, Google is telling the feds: No search items were found.

Good for Google.

Passed in 1998, COPA makes it illegal to post information that could be “harmful” to children who click their way to it. Nothing wrong with that concept, but, as the Supreme Court held last year, the legislation is unacceptably broad. Attitudes vary widely about what’s harmful to kids, and even if that problem could be solved, attempts to define “harmful” run a new batch of risks. You wind up fencing off “breast cancer” or “breast feeding” when you meant to sequester “Girls Gone Wild.”

The lawsuit that started the trouble has returned to a federal court in San Jose, and the Justice Department believes the search engine managers can help them make the government’s case. They are asking for a random list of a million Internet addresses that the search engine links to and a week’s worth of the words and strings of words computer users use in their searches.

If this were a criminal case in which the government were prosecuting a crime and could establish probable cause for going behind Google’s veil, different questions would come into play, and different answers. The public is willing to make reasonable compromises if that’s what it takes to protect actual victims from actual wrong-doers. In fact, however, the government merely wants to sift through mountains of data in hopes of backing up its contentions for the 3rd Circuit. Shouldn’t that kind of information have been collected before Congress passed the law in the first place?

The present concern is not primarily about invasion of privacy, although the potential shouldn’t be overlooked. The Justice Department isn’t seeking the names of people initiating the searches, just the aggregate information about what they’re looking for and where they’re sent to find it. Depending on what it does find, though, there’s no telling where it would drill next.

But the greater worry posed by this strategy is the precedent of enlisting a company like Google to do the Justice Department’s work. Americans who develop relationships with such an institution — an estimated 12 million Internet users a day conduct Google searches — shouldn’t have to worry that they’re opening their blinds for government peepers.

In anticipation of the obvious question, there are plenty of reasons to be concerned about the government sneaking into your private affairs, even if you’re totally law-abiding. The Founding Fathers’ fears about misuse of power by government have been validated countless times in the past two centuries.

The attempt to dispatch Google and other search engine managers to do the Justice Department’s legwork is the kind of situation the phrase “fishing expedition” was coined for. “Trawling” is more like it.