WASHINGTON, Aug 5 (Reuters) - Alphabet's

Google broke the law with monopolistic behavior over online

search and related advertising, a federal judge ruled on Monday,

the first victory for U.S. antitrust authorities who have filed

several lawsuits challenging Big Tech's market dominance.

The decision is a significant win for the Justice

Department, which had sued the search engine giant over its

control of about 90% of the online search market, and 95% on

smartphones.

"The court reaches the following conclusion: Google is a

monopolist, and it has acted as one to maintain its monopoly,"

U.S. District Judge Amit Mehta wrote.

His ruling paves the way for a second trial to determine

potential fixes, such as breaking up the company or requiring

the company to stop paying smartphone makers billions of dollars

annually to set Google as the default search engine on new

phones.

The "remedy" phase could be lengthy, followed by potential

appeals to the D.C. Circuit and U.S. Supreme Court. The legal

wrangling could play out into next year, or even 2026.

Shares of Google parent Alphabet fell 4.3% on

Monday as part of a broad tech share decline.

Alphabet said it plans to appeal Judge Mehta's ruling.

Mehta noted that Google had paid $26.3 billion in 2021 alone

to ensure that its search engine is the default on smartphones

and browsers, and to keep its dominant market share.

"The default is extremely valuable real estate... Even if a

new entrant were positioned from a quality standpoint to bid for

the default when an agreement expires, such a firm could compete

only if it were prepared to pay partners upwards of billions of

dollars in revenue share and make them whole for any revenue

shortfalls resulting from the change," Mehta wrote.

He noted "Google, of course, recognizes that losing defaults

would dramatically impact its bottom line. For instance, Google

has projected that losing the Safari default would result in a

significant drop in queries and billions of dollars in lost

revenues."

The ruling is the first major decision in a series of cases

taking on alleged monopolies in Big Tech. This case, filed by

the Trump administration, went before a judge from September to

November.

"A forced divestiture of the search business would sever

Alphabet from its largest source of revenue. But even losing its

capacity to strike exclusive default agreements could be

detrimental for Google," said Emarketer senior analyst Evelyn

Mitchell-Wolf, who noted a drawn out legal process will delay

any immediate effects for consumers.

In the past four years, federal antitrust regulators

have also sued Meta Platforms, Amazon.com, and

Apple Inc, claiming the companies have illegally

maintained monopolies. Another case against Google over its

advertising technology is scheduled to go to trial in September.

Speaking before the ruling, William Kovacic, a professor at

George Washington University Law School, said a DOJ victory is

likely to boost the morale of antitrust enforcers in other

cases.

"It's very good for their larger campaign to apply the

law effectively in this sector," he said.

When it was filed in 2020, the Google search case was the

first time in a generation that the U.S. government accused a

major corporation of an illegal monopoly. Microsoft settled with

the Justice Department in 2004 over claims that it forced its

Internet Explorer web browser on Windows users.