By Caroline Valetkevitch and Noel Randewich

NEW YORK/SAN FRANCISCO (Reuters) - Technology heavyweights might be all that keeps the U.S. earnings recession from extending into a fifth quarter in September if they hit the higher estimates Wall Street is calling for.

A bright spot in generally dour second-quarter results reported so far, technology is the only sector showing improved third-quarter analyst expectations, mostly because of strong scorecards recently from Facebook Inc <FB.O>, Google-parent Alphabet Inc <GOOGL.O>, Texas Instruments Inc <TXN.O> and others.

Analysts' third-quarter expectations for all other sectors have been deteriorating since last year on worries about slower global growth and the strength of the U.S. dollar, according to Thomson Reuters data, though profit growth still is expected in consumer discretionary, materials and other sectors.

Earnings across the S&P 500 are now seen growing just 0.2 percent in the third quarter over the same quarter a year ago, down from an estimate of 2 percent growth a month ago.

Technology profits, which this year have been the biggest contributor to S&P 500 earnings after financials, are now seen growing 3.1 percent in the third quarter, up from the 2.4 percent growth predicted a month ago.

Without the contribution of leaders like Alphabet and Microsoft Corp <MSFT.O>, for example, the entire index might show another quarter of slowing profit growth.

Investors have been predicting that S&P 500 aggregate earnings would start to grow again in the third quarter of this year after starting to shrink in the third quarter of 2015. The second quarter, mostly over, is on track to show a 2.4 percent decline.

Wall Street has been banking on fatter corporate profits to justify pricey valuations following a recent rally that has propelled the S&P 500 to record highs.

Part of the reason for strength in the tech sector may be related to the weight of just a few larger players. In 2015, Apple Inc <AAPL.O>, Microsoft, Alphabet, IBM <IBM.N> and Cisco Systems Inc <CSCO.O> pulled in combined earnings of $125 billion, equivalent to over half of all profits in the sector, according to a Thomson Reuters analysis.

"They have just become such powerful, dominant market players that they don't face quite the pressures of other companies," said Rick Meckler, president of LibertyView Capital Management in Jersey City, New Jersey.

"In the case of Facebook and Google, they continue to just steal share, advertising share, from traditional sources. So they are truly shifting the pie towards them," he said.

All those companies beat Wall Street's earnings expectations for the June quarter, except for Cisco, which is expected to report its quarterly results on Aug. 17. Its earnings per share beat expectations in at least the past eight quarters, according to Thomson Reuters data.

Tech's improving outlook has been noted on Wall Street, where the tech-heavy Nasdaq has risen 12 percent since its June 27 post-Brexit referendum low.

"Tech looks attractive," said Kristina Hooper, U.S. investment strategist at Allianz Global Investors. "Technology offers better values, especially when you factor in growth estimates."

(Reporting by Noel Randewich and Caroline Valetkevitch; Editing by Bill Rigby)