By Harshita Mary Varghese and Anhata Rooprai

Feb 6 (Reuters) - U.S. tech giants have predicted their spending would surge this year as they double down on artificial intelligence, sharpening investor scrutiny over whether these costly bets would generate enough returns to justify the sector's high valuations.

The group - including Alphabet, Microsoft, Amazon and Meta - is expected to pour more than $630 billion combined largely into artificial intelligence this year, even as returns so far have lagged the pace of growth in the outlays.

"Investors right now are not forgiving about large investments without clear signal on return on invested capital," analysts at Morgan Stanley said.

Below is a snapshot of how the companies fared in the December quarter:

CAPITAL EXPENDITURE

Amazon.com AMZN.O, once seen as a laggard in the AI race, is leading the charge with $200 billion reserved in spending. Alphabet is close behind with as much as $185 billion, while Meta has projected up to $135 billion.

CLOUD REVENUE

Google Cloud notched the fastest growth among the three major U.S. cloud providers in the reported quarter with a rise of 48%.

While the business is smaller than its major rivals, strong adoption of the latest Gemini model has led some analysts to say that Alphabet has taken the lead in the AI race.

Amazon Web Services - the largest cloud player - meanwhile posted a revenue growth of 24%, while Microsoft's Azure reported a 39% increase.

UNEVEN PROFIT

Rising expenses weighed on profit growth at Amazon and Meta in the quarter, while Microsoft reported its strongest profit growth in two years.

MARKET CAP GROWTH

Optimism about Gemini and Google's deal to power Apple's revamped Siri have also boosted Alphabet's share price, which has in recent months far outperformed its rivals.

(Reporting by Harshita Mary Varghese and Anhata Rooprai in Bengaluru; Editing by Sriraj Kalluvila)

((HarshitaMary.Varghese@thomsonreuters.com))