Updates with afternoon levels

By Ragini Mathur and Avinash P

July 22 (Reuters) - The S&P 500 edged higher on Wednesday, while technology shares struggled for direction as investors looked ahead to the first major Big Tech earnings reports to gauge the sustainability of the AI-driven market rally.

After months of gains that lifted the major indexes from their March lows, momentum has started to wobble, pressured by uneven trading in heavyweight semiconductor stocks.

The Philadelphia SE Semiconductor index .SOX rose 1.4%, though it had closed lower in five of the previous 10 sessions, highlighting fragile sentiment toward the chip sector.

Investors are now looking to second-quarter results from Alphabet GOOGL.O and Tesla TSLA.O, the first of the so-called "Magnificent Seven" megacap companies to report after the bell for fresh evidence that these companies' multibillion-dollar investments in AI are paying off.

Alphabet will be under particular scrutiny after a delay in the launch of a model central to its AI ambitions intensified concerns. Its shares were flat.

"Companies have to prove not only that they are growing, but that they are worthy of a premium valuation," said Bret Kenwell, U.S. investment analyst at eToro.

"Good reports right now are not good enough. They need to be great. And that's the market we're in right now."

Texas Instruments TXN.O, also due to report after the close, ticked 1.3% higher.

The S&P 500 information technology sector .SPLRCT swung between losses and gains. It was last up 0.3%, helped by a surge in AI-linked hardware names.

Super Micro Computer SMCI.O jumped 23.8% after the server maker said it had secured more than $60 billion in new orders in the fourth quarter. Peers Dell Technologies DELL.N and Hewlett Packard Enterprise HPE.N climbed 10% and 5.2%, respectively, after Super Micro also reported upbeat preliminary results.

The broader megacap complex was weaker, with Microsoft MSFT.O, Amazon AMZN.O, Apple AAPL.O and Meta Platforms META.O falling between 0.8% and 2.3%.

The crowded earnings calendar leaves markets vulnerable to sharper swings this week, while geopolitical tensions added another layer of caution.

Fighting in the Middle East remained in focus as threats to shipping by Yemen's Iran-backed Houthi militia, alongside a widening conflict, disrupted two of the world's most important energy chokepoints.

President Donald Trump vowed on Wednesday to destroy an Iranian bridge or power plant every time Iran shoots at a ship in the Strait of Hormuz.

Oil prices climbed to near six-week highs, complicating the outlook for central bankers.

The Federal Reserve is expected to keep interest rates steady for the rest of 2026, according to the median forecast in a Reuters poll of economists, though respondents said the risk of a rate hike remained elevated.

Traders are pricing in a nearly 72% chance the Fed leaves rates unchanged at next week's meeting, CME Group's FedWatch tool showed.

At 12:10 p.m. ET, the Dow Jones Industrial Average .DJI rose 190.81 points, or 0.37%, to 52,415.45, the S&P 500 .SPX gained 13.32 points, or 0.18%, to 7,522.52 and the Nasdaq Composite .IXIC lost 8.42 points, or 0.03%, to 25,828.26.

Among other movers, AT&T T.N rose 3.8% after the telecom firm added more wireless subscribers than expected in the second quarter.

Philip Morris International PM.N gained 3% after stronger cigarette demand helped the company beat quarterly results estimates.

Advancing issues outnumbered decliners by a 1-to-1 ratio on the NYSE, while declining issues outnumbered advancers by a 1.42-to-1 ratio on the Nasdaq.

The S&P 500 posted 13 new 52-week highs and one new low, while the Nasdaq Composite recorded 36 new highs and 68 new lows.