Investors are bracing for what could be a bellwether week for the stock market, with nearly a third of the 30 companies in the Dow Jones Industrial Average reporting quarterly earnings.

With so many companies posting results — about half of the S&P 500 index will also release numbers in the next two weeks — investors who have been jostled by the bulls and the bears in recent months may finally be able to determine whether the equity markets can withstand a slowing economy.

The markets ended last week on a strong note, with all three major indexes up more than 4%. If the trend holds over the next five days, the Dow could step into positive terrain for the first time this year. Starting off the spate of earnings is Bank of America, which is scheduled to release its numbers today before the opening bell. Analysts do not expect the country’s second-largest bank to meet its promise of increasing profit by 20% this year; instead, they predict earnings of $3.16 a share, a 28% drop from January, according to Bloomberg. The stock traded up 2.91%, to $38.56, on Friday.

“You are going to get disappointing earning from financial firms and anyone dependent on the domestic economy, like retailers, homebuilders, or airlines,” the president of Euro Pacific Capital, Peter Schiff, said.

A poor showing from Bank of America may not translate into a tanking market, however, as was seen on Friday when investors lapped up disappointing earnings from Citigroup. Despite posting a more severe first-quarter loss than most analysts had estimated, Citigroup stock closed up 4.5%, to $25.11 a share. The reason: In comparison with the fourth quarter, the results looked almost decent, bolstering investor confidence that the bank may have weathered the worst of the credit crisis. The same rationale could hold true for Bank of America, experts said.

Other companies expected to post earnings this week include the largest American credit card lender, New York-based American Express. While its shares closed Friday up 1.86%, to $45.53, the company may report worse than expected losses because of a recent wave of consumer defaults, an analyst at Friedman Billings Ramsey & Co., Scott Valentin, said. American Express cardholder defaults were the highest since 2004, excluding a sudden rise at the close of 2005 that resulted from a change in American bankruptcy laws, he said.

“Consumers are facing a tremendous amount of stress due to employment uncertainty, rising fuel and food prices, and declining home values,” Mr. Valentin said. He rates the company “underperform” and has reduced his 12-month price target 5%, to $38 a share.

Technology is also expected to have a big showing this week, with Microsoft, Yahoo, Amazon.com, and Apple all scheduled to release earnings.

Yahoo is facing what may be the most critical week of its existence, with an impending deadline for Microsoft’s unsolicited bid to buy the company for $31 a share and the release of its first quarter earnings scheduled for tomorrow. Yahoo has been fighting hard to get Microsoft to increase its bid, and its quarterly results could help determine whether that will happen, experts said. Analysts are expecting Yahoo to post a profit of around $0.09 a share, less than the $0.10 it earned a year ago.

Yahoo’s shares rose 1.43% on Friday, to $28.43, spurred in part by strong numbers from Google, which saw its shares jump nearly 20%, to $539.41, the company’s biggest one-day gain since it went public in 2004.

On Thursday, Microsoft will release earnings for its third quarter, the period in which it launched the bid for Yahoo. Analysts estimate that it will post strong gains, with earnings of $0.45 a share compared with $0.50 a share last year. Investors balked at Microsoft’s move in February to acquire Yahoo, with the company’s stock trading down roughly 10% since the bid was announced. It closed up 2.67%, to $30 a share, on Friday.

On Wednesday, both Apple and Amazon are expected to post strong quarterly earnings.

Helping to boost the tech sector may be its overseas activities, Mr. Schiff said. “Tech companies that have earnings from offshore businesses will look good, as they translate their earnings back into dollars,” he said. Mr. Schiff noted, however, that higher inflation is rendering these dollars “less valuable, so it really doesn’t do shareholders any good.”

Other companies scheduled to report results this week include Merck, McDonald’s, Boeing, and AT&T.