NEW YORK — 2011 was shaping up to be a washout for the stock market just two weeks ago. Now, it’s within shouting distance of its biggest comeback in nearly three decades. The Standard and Poor’s 500 index has jumped 11.4 percent since hitting its lowest level of the year on Oct. 3, largely because investors have become more confident that Europe will shelter its banks from huge losses on Greek bonds should that country’s government stop making payments on its debt. For much of the summer, investors feared that a Greek default could lead to a freeze of lending between European banks and cascade into a credit crisis similar to the one in 2008.

The S&P 500 was down 12.6 percent for the year as of Oct. 3, when it closed at 1,099. As of Friday, it had trimmed the loss to 2.6 percent. It needs to gain just 33 points, or 2.8 percent, to get above 1,257, where it started the year.