NEW YORK – Back to reality for the stock market – and back down.

Wall Street focused Wednesday on the bleak landscape ahead for the economy and sold off, wiping out the big gains from a day earlier and then some. The Dow Jones industrial average closed down 519 points.

The selling was intensified by worries about debt problems in Europe.

On Tuesday, the Federal Reserve said it planned to keep interest rates ultra-low for two more years. After some initial confusion, the stock market staged a huge comeback and had one of its best days.

But the interest-rate news proved to be a distraction. The Fed made the pledge because it sees almost no chance that the economy will improve substantially by 2013, and when investors focused on that, they dumped stocks again.

“Now it gets back to the fundamentals,” said Mark Lamkin, founder of Lamkin Wealth Management, which manages $215 million.

The Dow closed at 10,719.94, down 4.6 percent for the day. By points, it was the ninth-steepest decline for the market. The Dow has now lost more than 2,000 points in less than three weeks.

Wednesday was another day marked by big moves. The Dow was down more than 300 points within minutes of the opening bell. It recovered some of that loss, then drifted steadily lower in the last two hours.

The market has traded that way for two weeks, lurching up and down. The most extreme example was Tuesday, when the Dow swung more than 600 points in the one hour and 45 minutes after the Fed’s statement.

The stomach-churning highs and lows are reminiscent of the fall of 2008, the depths of the financial crisis, when swings of 800 or even 1,000 points in a day were not unheard of.

Computerized trading systems – programmed to analyze charts, capitalize on the tiniest changes in price and execute trades with no human intervention – are making the market rougher.

High-frequency trading programs make up about half the trades in a normal market day but 70 percent or more on a volatile one. The programs pounce on stock changes to make just slivers of a penny but do it so often that it adds up to real dollars.

Other investors also use charts and market indicators to make trades based on market momentum. The bet is that if the market is rising, it will keep rising, and if it’s falling, it will keep falling.

More investors are turning to this strategy because the sudden slowdown has left them unable to judge companies based on their fundamentals, such as projected profits. The more people use a momentum strategy, the faster the decline.

The S&P 500 finished the day down 4.4 percent, and the Nasdaq composite index down 4.1 percent.

Financial stocks led the market lower.

Bank of America and Citigroup each lost more than 10 percent of their market value. Wall Street is worried because it doesn’t know how badly American banks might be hurt by Europe’s debt problems.

Investors fear Italy and Spain will be the next countries unable to repay their debts. The European financial system has been battered by fears about banks holding bonds of heavily indebted countries such as Greece and Portugal.

“It’s the same game of Old Maid playing out in Europe that was played out here during the subprime mortgage crisis,” said Quincy Krosby, an economist and market strategist with Prudential Financial.

The fear is that if European governments default on their bonds, it will hurt the European banks that own them.