* S&P 500, Nasdaq start second quarter with losses
* Ford, GM report lower March sales
* ADP data misses estimates, raising payroll concerns
* Indexes down: Dow 0.4 pct, S&P 0.4 pct, Nasdaq 0.4 pct (Updates to close)
By Caroline Valetkevitch
NEW YORK, April 1 (Reuters) - U.S. stocks eased on Wednesday as weaker-than-expected economic data spurred concerns over growth ahead of Friday's jobs report and first-quarter earnings.
Leading the day's declines for a second day was the S&P health care sector, which fell 1.2 percent. Health care was the strongest sector in the first quarter, appreciating 6.2 percent.
Shares of automakers also declined after reporting March sales. Shares of General Motors were down 2 percent at $36.74 while Ford was down 1.4 percent at $15.91 as sales dipped at both companies.
U.S. private employers added the smallest number of workers in more than a year in March and factory activity hit a near two-year low, fresh signs that economic growth slowed significantly in the first quarter.
The reports precede Friday's jobs data, the most widely watched indicator of the week, though that arrives on Good Friday when the stock market will be closed.
Investors also are anxious ahead of the start of first-quarter earnings, which strategists say could be hurt by the rising dollar's impact on multinational companies. Estimates for first-quarter earnings have fallen sharply since Jan. 1, Thomson Reuters data showed.
"People continue to have concerns about earnings weakness and economic weakness," said Stephen Massocca, chief investment officer at Wedbush Equity Management LLC in San Francisco.
The Dow Jones industrial average fell 77.94 points, or 0.44 percent, to 17,698.18, the S&P 500 lost 8.2 points, or 0.4 percent, to 2,059.69 and the Nasdaq Composite dropped 20.66 points, or 0.42 percent, to 4,880.23.
The S&P 500 and Nasdaq finished their ninth straight quarter of gains on Tuesday, while the Dow dipped for the quarter.
Shares of Monsanto were up 3.9 percent at $116.96 and the stock was among the biggest positive influences on the S&P 500 after its results and forecast.
Energy shares also gained along with oil prices. ConocoPhillips was up 1.2 percent at $63.02.
NYSE advancing issues outnumbered declining ones 1,621 to 1,416, for a 1.14-to-1 ratio; on the Nasdaq, 1,449 issues fell and 1,280 advanced, for a 1.13-to-1 ratio favoring decliners.
The benchmark S&P 500 posted 7 new 52-week highs and 4 new lows; the Nasdaq Composite recorded 76 new highs and 59 new lows.
About 6.9 billion shares changed hands on U.S. exchanges, above the 6.5 billion daily average for the last five trading sessions, according to BATS Global Markets. (Editing by Bernadette Baum and Nick Zieminski)