NEW YORK (CNN/Money) - From the snowbanks of North Dakota to the muddy back roads of South Carolina, it's a frustration familiar to many American drivers: vehicle immobilized, tires spinning furiously, but finding no purchase in the snow or mud.

Last week, Fed Chairman Alan Greenspan pronounced that the U.S. economy, which had recently hit such a snowy, or muddy -- or "soft," in Greenspan's words -- patch, had regained some "traction."

While most economists agreed, last week's economic news made their case tougher.

A closely watched index of leading economic indicators fell for the third straight month. Consumer confidence slid. Weekly jobless claims rose. Orders for long-lasting durable goods fell. Sales of pre-owned homes weakened. Oil approached $50 a barrel again. [For a list of this week's key reports and events, click here.]

If the Fed didn't believe the data, Wall Street seemed to. The Dow Jones industrial average lost some 2.6 percent on the week. The Nasdaq and the S&P 500 each lost 1.6 percent.

This week, with few companies reporting earnings and little economic news until the end of the week, stocks could struggle to regain traction. Instead, they could be batted back and forth by end-of-quarter portfolio-shuffling by money managers and by the vagaries of the oil market.

Since some money managers may want to pad their portfolios with winners at the end of the quarter, stock sectors that have done well this year, such as energy, telecommunications and utilities, could thrive early this week, according to Paul Nolte, director of investments at Hinsdale Associates.

"But that's more of a short-term phenomenon than anything worth paying a lot of attention to," Nolte said. In the long run, "it's going to come down to better economic numbers."

If oil prices -- and wholesale gasoline prices -- continue to gain this week, the pain will be widespread.

Higher oil prices act as a sort of tax on consumers, leaving them less money to spend on other stuff. It also adds to the cost of doing business, giving corporate financial officers yet another reason to be tight-fisted about spending and hiring.

"While companies have bigger stacks of chips to play with, they still remain hesitant to put many of them into the pot," Carl Tannenbaum, chief economist at LaSalle Bank, wrote in a note to clients on Friday.

But even oil prices could be a short-term issue. Energy prices are volatile and have been pushed up by the disruptive effects of Hurricane Ivan. If oil and gas prices fall, then the economy could strengthen. Otherwise ...

"We are hopeful this will prove temporary, but the longer it lasts, the bigger is the risk that October -- which we have been pencilling in as the starting point for [a] recovery in [consumer] spending -- will disappoint," Ian Shepherdson, chief U.S. economist for High Frequency Economics, wrote in a note on Friday.

Thursday and Friday will bring some key economic reports, including measures of consumer income and spending and the Institute for Supply Management's closely watched manufacturing index.

The end of the quarter, though, will also bring us closer to the second anniversary of the bull market which began in early October 2002. If history is any guide, that could mean the best days are over for stocks, according to Sam Stovall, chief investment strategist at Standard & Poor's.

Stovall's research shows that, since 1942, the S&P 500 has posted average gains of just 3 percent in the third years of bull markets, compared with 38 percent in the first year and 12 percent in the second.

Of course, history is not always such a great guide. In the third year of the 1990-2000 bull market, stocks jumped 13 percent.

Key events in the week ahead:

• Monday morning brings the National Association of Realtors' report on new home sales in August. Economists, on average, expect the pace sales to increase to a 1.15-million-unit annualized rate, compared with 1.13 in July, according to Briefing.com.
• On Tuesday morning, the Conference Board, a private research firm, releases its figures for consumer confidence in September. Economists expect confidence to jump to 100 from 98.2 in August.
• Tuesday afternoon, Kansas City Fed President Thomas Hoenig, a voting member of the Fed's policy committee, speaks about monetary policy in Albequerque, N.M.
• Wednesday morning brings the Commerce Department's second revision of second-quarter gross domestic product (GDP) growth. Economists expect growth to be revised to a 3-percent annualized rate, compared with 2.8 percent in the first quarter.
• Thursday morning, the Labor Department will release the number of new claims for unemployment benefits in the week ending Sept. 25. Claims jumped to 350,000 the prior week, affected in part by hurricanes in previous weeks.
• Separately Thursday morning, the Commerce Department will release its figures for personal income and spending in August. Economists expect spending to rise 0.1 percent, compared with 0.8 percent in July, and they expect income to rise 0.4 percent, compared with 0.1 percent in July.
• Later Thursday morning, the NAPM-Chicago will release its index of Chicago-region business activity in September. Economists expect the Chicago PMI to rise to 58 from 57.3 in August.
• Also Thursday morning, the Conference Board releases its Help Wanted Index, a measure of newspaper job advertising, for August. Economists expect the index to hold steady at 37.
• Friday morning, the Institute for Supply Management releases its manufacturing index for September. Economists expect the ISM to dip to 58.3 from 59 in August.
• Separately on Friday morning, the University of Michigan releases its revised consumer sentiment index for September. Economists expect sentiment to rise to 96.5 from an initial reading of 95.8.