Google can use any criteria it wishes to rank websites, including downgrading competitors, a lawyer for the search giant has told a US federal judge.

KinderStart.com is suing Google because, it said, the company gave KinderStart's site a zero ranking in its PageRank system and blocked the site. KinderStart's site, which provides information about parenting and related topics, including its own specialised search page, suffered a major drop in visits as a result, it claimed. The company wants to pursue the case as a class action on behalf of other websites that have suffered because they were blocked or given low PageRank numbers.

At a hearing in the US District Court for the Northern District of California, in San Jose, Judge Jeremy Fogel heard arguments about a Google motion to dismiss the case.

Among other things, KinderStart said Google has defamed it, kept it from expressing itself in a public forum, and violated KinderStart's contract under Google's AdSense program, in which it carries ads distributed by Google and gets a commission when users click on them. KinderStart calls itself a competitor to Google in the specific area where it offers search results. As part of the suit, it wants Google to reveal how it comes up with its rankings.

Google said its search rankings are opinions and entitled to free-speech protection.

Although rankings were based partly on a mathematical algorithm, Google also studied the quality of sites and made subjective judgments, an attorney from Wilson Sonsini Goodrich & Rosati who is representing Google, David Kramer, said.

Any Google user knows the rankings are opinions, and Google could make them using any criteria it wants - including giving poor rankings to competitors - without telling users, Kramer said. He didn't concede that Google actually downgraded competitors. If KinderStart could sue Google because the search engine didn't give its site enough promotion, there was nothing to stop archrivals Microsoft or Yahoo from doing the same thing, Kramer argued.

Judge Fogel was skeptical about KinderStart seeking to have Google's ranking criteria produced as evidence.

"You can't just file a blanket lawsuit and say, 'We think we're going to find some stuff,'" Fogel said.

Google's position as a collector and arbiter of all sorts of information gave it unprecedented power, KinderStart's attorney in the case, Gregory Yu, said.

The judge's next step will be to rule on what parts of KinderStart's case, if any, can go forward. He set a September 29 hearing on a separate motion by Google, in which the company wants to strike some claims from KinderStart's suit on the basis of a California law against suits that stifle a defendant's free speech rights. At that hearing he would also hear KinderStart's arguments for a preliminary injunction to make Google restore the company's site to its index while the case was heard.