Wall Street posts worst week since June, banks weigh

Traders work on the floor of the New York Stock Exchange, October 12, 2012.

NEW YORK (Reuters) - U.S. stocks wrapped up their worst week in four months, led lower on Friday by financial shares as results from Wells Fargo and JPMorgan ignited concerns about shrinking profit margins for big lenders.

Shares of Wells Fargo (WFC.N) fell 2.6 percent to $34.25 and JPMorgan Chase & Co (JPM.N) lost 1.1 percent to $41.62 as concerns grew over their lower net interest margin - the difference between what a bank pays on deposits and what it makes on loans - which could narrow further as the Federal Reserve keeps interest rates near zero.

The lackluster market reaction came even though both Wells Fargo and JPMorgan, the two largest U.S. financial stocks by market value, reported record profits.

"Bank shares as a group have had a nice move (up) this year so far," said Ken Polcari, managing director at ICAP Equities in New York. "Guidance is cautious so people are taking money off the table."

The results sparked a selloff in other bank shares. An S&P financial index, down 1.4 percent, represented the worst performer of the S&P 500's top 10 sectors. The KBW Bank index lost 2.5 percent.

Polcari said the low volume that came with this week's decline indicated this was not a sign of panic. Since hitting a near five-year intraday high of 1,474.51 on September 14, the benchmark S&P 500 Index has fallen 3.1 percent.

"If we keep getting negative reports, selling will pick up," he said.

Expectations are low for S&P 500 companies' results. Quarterly earnings are forecast to fall 3 percent from a year ago, compared with a 2.1 percent drop estimated at the start of the month, according to Thomson Reuters data.

The Dow Jones industrial average edged up 2.46 points, or 0.02 percent, to 13,328.85 at the close. But the S&P 500 fell 4.25 points, or 0.30 percent, to finish at 1,428.59. The Nasdaq Composite dipped 5.30 points, or 0.17 percent, to 3,044.11.

The S&P 500 closed right above its 50-day moving average, barely enough to avoid going into the weekend with a technical red flag hanging over the market.

Despite several encouraging data points this week, the benchmark S&P 500 fell 2.2 percent - its worst weekly performance since the week ended June 1.

Shares of Workday Inc (WDAY.N), a cloud computing company that has yet to turn a profit, soared nearly 74 percent to $48.69 in their market debut, driving some tech analysts to question the lofty valuation.

Advanced Micro Devices Inc (AMD.N) fell 14.4 percent to $2.74 a day after the chipmaker said its third-quarter revenue probably fell 10 percent from the previous quarter as a weak global economy and a growing preference for tablets slams the PC industry.

About 5.5 billion shares changed hands on the New York Stock Exchange, the Nasdaq and NYSE MKT, below the daily average so far this year of about 6.52 billion shares.

On the NYSE, about seven issues fell for every four that rose. On the Nasdaq, almost two issues fell for every one that advanced.

Earlier in the session, the market was supported by Thomson Reuters-University of Michigan data showing U.S. consumer sentiment unexpectedly rose to its highest in five years in October, in the latest in a string of encouraging signs about the economy.

(Reporting by Rodrigo Campos; Editing by Jan Paschal)