NEW YORK — It’s the best start for stocks in 15 years.

The Dow Jones industrial average and the Standard & Poor’s 500 each finished with their biggest January gains since 1997. Stocks jumped on the first trading day of the year and made a slow climb from there.

There was a dip at the end, though. The Dow fell 21 points today to close at 12,632. Traders were discouraged by unexpectedly weak consumer confidence figures. The S&P closed down a fraction of a point, and the Nasdaq gained two.

Advancers and decliners were about even on the New York Stock Exchange. Volume was a little higher than average lately at 4.1 billion shares.

The S&P ended the month up 4.4 percent.

Investors had such low expectations for the economy that it was easy for reports in January to come in better than expected, said Jerry Harris, chief investment strategist at the brokerage Sterne Agee.

But the news has mostly been good. Unemployment has fallen from a 10 percent peak in October 2009 to 8.5 percent, and the economy grew at a faster clip each quarter last year.

“I don’t see anything really glamorous or tremendous about the economy or earnings,” Harris said. “But I think they’re very acceptable, and things are grinding along.”

The Dow closed at 12,217.56 at the end of last year, then started this year with a pop — a gain of 179.82 points on opening day. It was the kind of big swing investors became accustomed to in 2011.

Since then, it’s been a quiet ascent: 19 days in a row of moves of less than 100 points. The last time the Dow had such a placid stretch was a 34-day run that started Dec. 3, 2010.

“Companies are reporting barely any increases in revenues and are just barely beating earnings forecasts. There are no big surprises,” said Kim Caughey Forrest, a senior equity analyst at money manager Fort Capital Group. “That’s the kind of ho-hum economy that we are in right now.”

Today, the Dow started up 66 points after encouraging signs from Europe that Greece might finally complete a deal to cut its crushing debt, a step toward securing a critical €130 billion bailout payment.

Greece is negotiating with investors who bought its government bonds. They are expected to swap their bonds for new ones with half the face value, plus a lower interest rate and longer term of maturity.

Investors are increasingly worried that Portugal may need a similar deal with its private creditors. European leaders insist the Greek reduction is a one-time event. Portugal’s borrowing costs have risen to record highs.

The Dow lost its gains after the Conference Board reported that its consumer confidence index fell to 61.1 in January, down from 64.8 in December. Economists had expected 68.

There were also signs that the housing market continues to struggle. Home prices fell in November for a third straight month in in 19 of the 20 cities tracked by the S&P/Case-Shiller index. The biggest declines were in Atlanta, Chicago and Detroit.

Six of the 10 major categories in the S&P 500 were lower for the day. Telecommunications stocks, financial stocks, utilities and information technology stocks managed small gains.

Avery Dennison Corp., which makes labels and packaging materials, was the worst performer in the S&P, down 5.7 percent, after it said earnings plunged 81 percent on nearly flat sales. Its 2012 outlook was well below Wall Street expectations.

RadioShack Corp. stock plummeted 28 percent after the company said its profit fell sharply — 11 cents to 13 cents per share for the quarter that ended in December, down from 51 cents a year earlier and less than half what Wall Street was expecting.

Best Buy Co. Inc., one of RadioShack’s competitors, responded by falling 5.2 percent, among the S&P worst. Both companies sell and service cellphones, but demand has softened at their stores.

Among other stocks in the news:

— Mattel Inc. soared 5.2 percent because of strong demand for Barbie and Monster High dolls during the holidays. That boosted Mattel’s fourth-quarter profit by a better-than-expected 14 percent. The company also raised its dividend.

— U.S. Steel Corp. gained 4 percent after it reported strong demand for pipes from the oil industry from October through December. The company was also optimistic about this quarter.

— Agriculture conglomerate Archer Daniels Midland declined 4.6 percent after it reported an 89 percent drop in quarterly net income. The company said its results were weighed down by weakness in oilseeds, corn processing and agricultural services.

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