Federal Judge Amit Mehta, whose decision is not expected until later in the year, raised his questions during two days of hearings that come six months after the conclusion of testimony.

The case is the first of five major lawsuits by the US government to reach trial, with Meta, Amazon, Apple and a separate case against Google also heading for federal court.

The trial is the first time the US Department of Justice (DOJ) has faced a big tech company in court since Microsoft was targeted more than two decades ago over the dominance of its Windows operating system.

The decision in the search engine case will be made by Judge Mehta, who presided over several months of testimony that saw Google CEO Sundar Pichai and other top executives take the stand.

At the heart of the government's case is the massive payments made by Google to Apple and other companies to keep its world-leading search engine as the default on iPhones, web browsers and other products.

The trial revealed payments reaching tens of billions of dollars every year for Google to keep its prime real estate on Apple hardware or the Safari and Mozilla browsers.

In 2022, Google paid Apple $20 billion for the default status, trial documents unsealed this week showed.

DOJ lawyers allege that Google achieved and perpetuated its dominance -- and strangled rivals -- through these default deals that also expanded to Samsung and other device makers.

But Judge Mehta expressed doubts that the case had sufficiently demonstrated the negative consequences necessary to deem the deals anti-competitive according to US law and precedent.

The key precedent is the landmark Microsoft case, which helped define how a tech platform can illegally abuse its monopoly to punish rivals.

But Mehta inferred that the Google case was very different from Microsoft's as it did not involve agreements to outright exclude competing browsers and other products.

"This case is different" because the user of an iPhone has the option to download and use rival apps, Mehta said.

"You have to show actual anti-competitive effects. You have to establish foreclosure first and if you can't, you lose," Mehta told the US government lawyers.

- Billions to Apple -

Mehta also poked holes in Google's defense, wondering how any rival search engine with a similar quality product could win access to the default deals if the cost would require tens of billions of dollars.

"Even if they can meet on that (quality) battlefield, they then would have to spend billions more to make Apple whole," Mehta said.

Mehta also focused questions on whether search queries on Amazon, Facebook or Expedia competed with Google, as argued by the tech giant.

Including activity on those websites would damage the US case, which rests on maintaining that general search, in which Google has over 80 percent of the US market share, is the relevant market.

Mehta also homed in on Google's contention that DuckDuckGo, the privacy focused search engine, was a competitor.

"You really think that DuckDuckGo is a competitor on Google?" Mehta asked Google's lawyer, who insisted that it was.

Lawyers from the Justice Department also faced pointed questions, with Mehta rejecting the idea that Google's dominance has stifled innovation for search.

That would be "a hard road for you to go down", the judge warned.