American stocks rose after a rally in computer and consumer shares lifted the Dow Jones Industrial Average 150 points in the last 20 minutes of trading.

Apple Inc. and Cisco Systems Inc. climbed and computer shares added the most to the advance in the Standard & Poor’s 500 Index. Merck & Co. helped carry the Dow to its largest gain since July 12 on prospects for expanded use of a vaccine.

The Dow average erased a 79-point drop spurred by concern mortgage losses are spreading after Bear Stearns Cos. suspended withdrawals from a hedge fund. The S&P 500 climbed after falling below its 200-day moving average for the first time in a year.

“At some point people finally decided unless everything in the world suddenly goes bad here, this is a good time to get in,” Ernie Ankrim, who helps manage about $200 billion as chief investment strategist at Russell

The S&P 500 increased 10.54, or 0.7%, to 1465.81. The Dow average added 150.38, or 1.1%, to 13,362.37. The Nasdaq Composite Index increased 7.6, or 0.3%, to 2553.87.

The S&P 500 switched between gains and losses at least 33 times. Some 2.4 billion shares changed hands on the Big Board, 49% more than the three-month daily average.

Apple added $3.24 to $135. Analysts at Citi Investment Research recommended investors buy the stock, saying a 6.8%decline Tuesday was overdone. Macintosh sales should remain “strong” through the year, they predicted.

Cisco, the biggest maker of computer-networking equipment, climbed 86 cents to $29.77.

Merck & Co. Inc. rose $1.37 to $51.02. Vaccines made by the company and Sanofi-Aventis SA are being promoted by American health officials to increase potentially life-saving immunization for preteens.

A gauge of consumer shares made the second-largest contribution to the S&P 500’s advance.

Whole Foods climbed $2.48 to $39.52 after profit topped analysts’ estimates, the second-best gain in the S&P 500.