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* Futures: Dow up 0.08%, S&P down 0.52%, Nasdaq down 1.23%

Jan 31 (Reuters) - Nasdaq futures slid over 1% on Wednesday as rising AI cost projections from tech giants Alphabet and Microsoft disappointed investors, driving a slide in megacap and chip stocks, while all eyes were on the U.S. policy decision expected later in the day.

Alphabet slumped 5.6% in premarket trading after the company reported holiday-season advertising sales below expectations and projected higher spending this year on items such as servers to power artificial intelligence.

Microsoft, too, lost 1.5% after forecasting rising costs to develop new artificial-intelligence features that eclipsed a quarterly results beat.

"In the case of Alphabet, and perhaps Microsoft as well, the market is now getting the jitters that AI investments are going to keep piling up," said AJ Bell investment director Russ Mould.

"These companies have been signaling for a while that investment was needed, but it seems to have fallen on deaf ears until now."

These results and forecasts, coupled with Tesla's growth warning last week, have prompted renewed focus on risks from the outsized weighting of the so-called "Magnificent Seven" stocks' in the S&P 500, that have collectively pushed the benchmark index to record highs.

Apple, Meta Platforms and Amazon.com , set to deliver their earnings on Thursday, fell between 0.7% and 2.7%. Together they comprise Magnificent Seven with Tesla, Microsoft, Alphabet and Nvidia.

Advanced Micro Devices tanked 6.6%, as the chipmaker's first-quarter revenue forecast and a boosted projection for AI processors by $1.5 billion failed to meet expectations.

Other chip stocks Nvidia, Intel, Broadcom and Marvell Technology declined between 1.1% and 2.7%.

Among other major earnings, Boeing, Mastercard , Phillips 66 and Thermo Fisher Scientific are due before market open, while Qualcomm and Align Technology are expected after market close.

About 78.5% of the S&P 500 companies that have reported earnings thus far have surpassed expectations, compared with a long-term average of 67%, according to LSEG data on Tuesday.

The focus was now on the Federal Reserve's first monetary policy decision this year, at 2 p.m. ET, widely expected to hold rates steady.

With an improved inflation outlook upping the possibility of policy easing sooner than later, investors will be scavenging for any hints on when the first U.S. rate cut might arrive this year, another key element that could determine the fate of the heavily weighted tech and tech-adjacent stocks.

The ADP National Employment report for January, due before market open, will also be parsed for further insights into the U.S. labor market's strength after the JOLTS report on Wednesday signaled an unexpected rise in December job openings.

At 5:21 a.m. ET, Dow e-minis were up 32 points, or 0.08%, S&P 500 e-minis were down 25.75 points, or 0.52%, and Nasdaq 100 e-minis were down 216.25 points, or 1.23%.

Among others, Tesla shed 2.9%. A Delaware judge tossed out Elon Musk's record-breaking $56 billion Tesla pay package.

Mondelez International lost 2.8% as price hikes took a toll on volumes, squeezing demand for the Cadbury parent's chocolates and salty crackers. (Reporting by Ankika Biswas in Bengaluru; Editing by Shinjini Ganguli)