* Labor market, service sector data could set payroll tone
* Crude oil jumps above $100 per barrel on unrest in Egypt
* S&P 500 struggling to break through 50-day moving average
* Futures down: Dow 103 pts, S&P 500 8.4, Nasdaq 17.75
NEW YORK, July 3 (Reuters) - U.S. stock index futures fell on Wednesday, tracking international weakness amid concerns about the pace of global economic growth, ahead of key U.S. data and an abbreviated pre-holiday trading session.
Shares in China fell after a read on the country's services sector compounded concerns about slowing growth momentum, while European shares tumbled amid a political crisis in Portugal that sent the country's bond yields soaring.
Traders were looking to the release of a flurry of economic indicators in the United States, including on the labor market and services sector, which could give insight into the strength of Friday's closely watched payroll report.
If the data is weak, it may have an outsized impact on financial companies, which are closely tied to the pace of economic growth. Bank of America fell 0.9 percent to $12.79 in premarket trading.
Many market participants are out of the office for the Fourth of July holiday, with U.S. financial markets closing early on Wednesday and reopening on Friday.
"There's a perfect storm of bad news out there, and things could get very sloppy today," said Art Hogan, managing director at Lazard Capital Markets in New York. "And with the (upcoming) holiday, trading volumes will be down, which means any moves could be exaggerated."
S&P 500 futures fell 8.4 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures lost 103 points and Nasdaq 100 futures fell 17.75 points.
The S&P 500 is 3.3 percent below its May 21 record closing high of 1,669.16, but has been unable to close above its 50-day moving average of 1,623.94 since June 20.
The ADP national employment report will be released at 8:15 a.m. EDT (1215 GMT) and is expected to show 160,000 private sector jobs added in June, an increase of 25,000 from the previous month. Weekly jobless claims, due at 8:30 a.m. (1230 GMT), are seen dropping by 1,000 to 345,000 in the latest week.
The Institute for Supply Management's June read on the services sector will also be closely scrutinized. The report is seen coming in at 54, compared with 53.7 in the previous month.
Economic data has been a significant market mover in recent weeks as investors attempt to gauge when the U.S. Federal Reserve will begin pulling in its bond-buying stimulus program, which has been credited with fueling the market's gains this year. Bullish data has led to market declines as traders worry a strong economy will mean a faster end to the policy.
In the upcoming nonfarm payroll report, analysts expect 165,000 jobs to have been added in June, below the 175,000 added in May.
Crude oil prices rose 1.4 percent to $100.99 a barrel, a 14-month high, on concerns that political unrest in Egypt could destabilize the Middle East and disrupt supply.
"The spike in oil may act as a near-term positive for energy companies, but this isn't related to increased demand, so there's no economic benefit to it," said Lazard's Hogan.
Insurance companies will be in focus after the Obama administration said it wouldn't require employers to provide health insurance for their workers until 2015, delaying a key provision of the healthcare reform law by a year.
In corporate news, Michael Dell has been advised to raise his $24.4 billion offer for Dell Inc, coming under further pressure as billionaire investor Carl Icahn revealed he had committed more than $3 billion to back an alternative proposal.
Avon Products Inc sold its Silpada Designs jewelry business for $85 million, three years after buying it for $650 million.