* S&P 500 on track for biggest weekly decline of 2013
* Jobs report on tap, weak payrolls could spark decline
* F5 Networks plunges in premarket after weak outlook
* Futures down: Dow 90 pts, S&P 10.7 pts, Nasdaq 20.5 pts
NEW YORK, April 5 (Reuters) - U.S. stock index futures fell on Friday as investors looked to the release of nonfarm payrolls data, which could be the latest in a series of reports pointing to slowing growth.
Analysts expect 200,000 jobs to have been added in March, down from 236,000 added in February. The unemployment rate is expected to remain at 7.7 percent.
Equities have struggled for direction since the S&P 500 reached an all-time closing high earlier this week, and a disappointing report may trigger a more protracted sell-off. The S&P is down 0.6 percent so far this week, on track to be its worst week of 2013.
Earlier this week, private sector employment and jobless claims data indicated weakness in the labor market. Reports on the manufacturing and services sectors also disappointed.
"The tone in markets could change if we get a positive surprise, but the data we've seen leading up to this has people expecting fewer job gains than we've been seeing," said Chris Bertelsen, chief investment officer of Global Financial Private Capital in Sarasota, Florida, adding the report could come in as low as 100,000 jobs, half the estimate.
Investors will likely be looking for the payrolls report to meet expectations. Stronger numbers than expected could raise concerns that the Federal Reserve may slow its economic stimulus programs sooner than anticipated.
Central bank actions around the world have boosted equities thus far this year, and lifted the S&P about 9.4 percent. On Thursday, Wall Street rose after the Bank of Japan announced aggressive policies to jump-start its economy.
S&P 500 futures fell 10.7 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 sank 90 points and Nasdaq 100 futures lost 20.5 points.
If the S&P closes down on the week, it will be only the third weekly loss this year for the benchmark index, which has struggled to surpass an intraday record high of 1,576.09.
Energy shares have been among the most pressured recently, dropping alongside crude oil, which is down 4.6 percent this week. Tied to growth expectations, the group could continue to struggle if the payroll report disappoints. Chevron Corp has lost 2.6 percent over the past two weeks.
Overseas, European shares slumped 1.5 percent, falling to a one-month low on concerns over growth and a decline in airline shares.
"A lot of the weakness in Europe is being carried over here," said Bertelsen, who helps oversee $2.1 billion in assets.
Earnings forecasts have declined heading into first-quarter reports, due to be kicked off next week by Alcoa. S&P 500 earnings are expected to have risen just 1.6 percent from a year ago, according to Thomson Reuters data, down from 4.3 percent forecast in January.
* Late Thursday, F5 Networks Inc forecast second-quarter earnings and revenue that were well below expectations. Its shares slumped 17 percent to $75.20 in premarket trading.
* Geopolitical tensions will remain in focus after North Korea placed two of its intermediate range missiles on mobile launchers and hid them on the east coast of the country, South Korean media reported on Friday.