By Diane Bartz

WASHINGTON Microsoft chief executive Satya Nadella on Monday took the witness stand in the U.S. Justice Department's once-in-a-generation antitrust fight with Alphabet's Google.

Nadella said that Microsoft, itself a tech powerhouse, had sought to make its Bing search engine the default on Apple smartphones but was rebuffed.

Nadella dismissed an argument that Google has made, that it is easy to change defaults on devices, as "bogus".

"Changing defaults today is easiest on Windows and toughest on mobile," he said.

The government has argued that Google, worth more than $1 trillion with some 90% of the search market, illegally paid $10 billion annually to smartphone makers like Apple and wireless carriers like AT&T and others to be the default search engine on their devices. The clout in search makes Google a heavy hitter in the lucrative advertising market, boosting its profits.

Google has sought to show that the quality of its products are the reason for its success rather than illegal behavior.

Nadella became CEO of Microsoft in 2014, long after the tech giant had faced its own federal antitrust lawsuit. That court fight, which began in 1998 and ended in a 2001 settlement, forced Microsoft to end some business practices and opened the door to companies like Google.

As Google, which was founded in 1998, became an industry leading search engine, the two became bitter rivals. Both have browsers, search engines, email services and a host of other overlaps. They have recently become rivals in artificial intelligence, with Microsoft investing heavily in OpenAI and Google building the Bard AI chatbot among other investments.

(Reporting by Diane Bartz; editing by Christina Fincher)