WASHINGTON (Reuters) - The U.S. government will lay out its antitrust case against Alphabet's Google on Friday in a second day of closing arguments focused on accusations that the online search leader broke the law to stay on top in search advertising.

U.S. District Judge Amit Mehta on Thursday peppered both sides with questions seeking to better understand the case ahead of making a ruling.

The Justice Department has hammered away at Google in a trial that started on Sept. 12, arguing the search engine giant is a monopolist and illegally abused its power to boost profits.

On Friday, Google and the government's lawyers are expected to focus their arguments on claims that Google's business contracts harmed competition for search advertising.

Witnesses from Verizon, Android maker Samsung Electronics and Google itself testified about the company's annual payments - $26.3 billion in 2021 - to ensure that its search is the default on smartphones and browsers, and to keep its dominant market share.

Google has claimed that search advertising markets are competitive, but the government asserts that the tech giant manipulated ad auctions and could increase prices as wanted without fear of harming business.

Mehta is expected on Friday to take up the government's claim that Google intentionally destroyed internal documents that were relevant to the issues in the lawsuit. The government wants Mehta to presume that Google deleted chats that were unfavorable to the company.

Google has defended its data preservation practices, calling them reasonable, and urged the court not to sanction the company.

Google is expected to tell the court that its "search advertising technologies have proven to be incredibly valuable to advertisers" and that "search and search advertising quality and output have continually improved."

The court is not expected to issue an oral ruling at the conclusion of the argument.

This case, filed by the Trump administration, was the first of five aimed at reining in the market power of tech leaders.

The second, against Facebook parent Meta, was also filed during the Trump administration, while Biden's antitrust enforcers have followed with a second case against Google and cases against Amazon.com and Apple Inc.

(Reporting by Chris Sanders; Editing by David Gregorio)

By Mike Scarcella