* Data expected to show improved jobs growth
* S&P may be vulnerable after strong January gains
* Merck beat expectations, but full-year view tepid
* Futures up: Dow 63 pts, S&P 4 pts, Nasdaq 6.5 pts
NEW YORK, Feb 1 U.S. stock index futures gained on Friday as investors anticipated data that was expected to show that U.S. jobs growth picked up in January.
The non-farm payrolls report is expected to indicate that 160,000 jobs were added in January, from 155,000 a month earlier, in a sign of continued labor market recovery despite an unexpected contraction in fourth-quarter gross domestic product. The report is due at 8:30 a.m. EST (1330 GMT)
If the jobs figure is weaker than expected, the market could be vulnerable to a pullback, tipping the S&P 500 off its best monthly performance since October 2011. However, any losses could be limited as investors have been buying on dips over the past four weeks. The largest daily decline in the S&P 500 so far this year was Wednesday's 0.39 percent drop, after the GDP data.
"A disappointing report could mark the start to a minor correction as the market is more likely to consolidate at these levels, but the flows coming into equities would make any pullback shallow," said Paul Mendelsohn, chief investment strategist at Windham Financial Services in Charlotte, Vermont.
"Still, there is further room to rise, and if the report is strong, we could break through (resistance at) 1,510 on the S&P, which could allow us to work our way towards 1,530."
While Thursday's jobless claims report was weaker than forecast, many recent indicators, including the ADP employment report and personal income data, have pointed to stronger economic growth.
Dow component Merck & Co dipped 0.6 percent to $43 in light premarket trading after the company gave a cautious outlook on 2013, though its quarterly results beat expectations.
S&P 500 futures rose 4 points and were above 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 added 63 points, and Nasdaq 100 futures rose 6.5 points.
The S&P advanced 5.1 percent in January, with gains driven by a sturdy start to the earnings season and a compromise in Washington that postponed the impact of a "fiscal cliff" of automatic spending cuts and tax hikes that were due to take effect early this year.
So far this week, the Dow is down 0.3 percent, the S&P is off 0.3 percent, and the Nasdaq has dipped 0.2 percent.
While the payroll report will likely be the primary market driver, corporate earnings will stay in focus. Exxon Mobil Corp and Chevron Corp, both Dow components, are on tap to report on Friday.
"Earnings have been one of the strongest sectors during the recent rally, so Exxon and Chevron results will be especially important to gauge where the group is going from here," Mendelsohn said.
Of the 231 companies in the S&P 500 reporting earnings so far, 69.3 percent have exceeded expectations, according to Thomson Reuters data through Thursday morning. That is a higher proportion than over the past four quarters and above average since 1994.
Overall, S&P 500 fourth-quarter earnings rose 3.7 percent, according to the data, above a 1.9 percent forecast at the start of the earnings season but well below a 9.9 percent profit growth forecast on Oct. 1.
Other data due Friday include consumer sentiment, U.S. manufacturing, construction spending and car sales. January sentiment is seen edging slightly higher in the month while construction spending rises 0.6 percent in December.
U.S. stocks closed lower on Thursday amid investor caution ahead of the payroll report.
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