US STOCKS-Virus fears keep S&P 500, Dow subdued after strong quarterly rebound

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* Record COVID-19 surge in California, Texas

* Boeing tumbles after Norwegian Air cancels orders

* Uber up on report of potential bid for Postmates

* Indexes mixed: Dow off 0.19%, S&P up 0.20%, Nasdaq up 0.43% (Updates to open)

By Pawel Goraj and Devik Jain

June 30 (Reuters) - The S&P 500 and Dow Jones indexes were muted at the open on Tuesday as coronavirus-related worries and simmering U.S.-China tensions weighed on sentiment at the end of what is expected to be the S&P 500's best quarter since 1998.

The benchmark index has rebounded about 18% since April on a raft of fiscal and monetary stimulus and the easing of restrictions, but is still down about 5% on the year as a flare-up in virus cases fuels fears of a new round of lockdowns.

With California and Texas marking a record spike in cases on Monday, investors are counting on more stimulus to shore up the domestic economy.

Eight of the 11 major S&P 500 sub-indexes were trading slightly higher, with real estate and financial stocks leading gains.

"While traders remain curiously cautious waiting for the next catalyst, they are also keeping risk on a short leash into the long weekend," said Stephen Innes, markets strategist at AxiCorp.

"COVID-19 de-risking playbooks are still in play and investors are not aggressively buying dips while booking profit quickly."

Federal Reserve Chair Jerome Powell, who will testify before the U.S. House of Representatives Financial Services Committee at 12:30 p.m. ET, said in prepared remarks the outlook for the world's biggest economy was "extraordinarily uncertain".

Sino-U.S. tensions are heating up again with Washington beginning to eliminate Hong Kong's special status under U.S. law in response to China's national security law for the territory. China said it would retaliate.

"If the environment between the United States and China continues to deteriorate, the market is not going to be happy, but because very little has been known about what's going on with those new laws, it's not having much of an impact yet," said Robert Pavlik, chief investment strategist at SlateStone Wealth LLC in New York.

Meanwhile, kicking off a data-heavy week for Wall Street, consumer confidence is expected to have climbed to 91.8 in June from 86.6 in May. Data on manufacturing activity and employment are due on Wednesday and Thursday.

At 9:41 a.m. ET, the Dow Jones Industrial Average was down 48.89 points, or 0.19%, at 25,546.91, the S&P 500 was up 5.98 points, or 0.20%, at 3,059.22, and the Nasdaq Composite was up 42.80 points, or 0.43%, at 9,916.96.

In company news, Boeing Co tumbled 5.6% and was the biggest drag on the blue-chip Dow after Norwegian Air canceled orders for 97 aircraft and said it would claim compensation.

Micron Technology Inc jumped 6.4% as it forecast higher-than-expected current-quarter revenue on strong demand for its chips that power notebooks and data centers.

Uber Technologies Inc rose 3.5% after reports said the ride-hailing services company was in talks to buy food-delivery app Postmates.

Declining issues nearly matched advancers on the NYSE and the Nasdaq.

The S&P index recorded two new 52-week highs and no new low, while the Nasdaq recorded 22 new highs and four new lows. (Reporting by Pawel Goraj in Gdansk and Devik Jain in Bengaluru; Editing by Sagarika Jaisinghani, Sriraj Kalluvila and Arun Koyyur)