Investors expecting sluggish action during the final week of summer may be in for a surprise as a slew of heavy-duty economic data could unsettle a shaky market.

The

S&P 500

has slipped 2.5% this month and the

Nasdaq

has spent four straight weeks in the red. But while returns are often taken with a grain of salt in this vacation-heavy month, some traders are beginning to wonder if there is more to the selloff than a mere case of the light-volume blues.

"People are starting to wonder if this late-summer decline is for real," says Brian Williamson, equity trader at Boston Company Asset Management.

Williamson says the downward trend could be exacerbated if we get worse-than-expected economic numbers next week, because volume is typically light prior to Labor Day.

On Tuesday, the market will receive consumer confidence data for August. Economists expect confidence to dip to 102 from 103.2 the prior month, mostly due to higher energy costs.

Also on Tuesday are July factory orders and the minutes from the August

Federal Open Market Committee

meeting. Most market and Fed-watchers, however, are not expecting too much of a change in the Fed's language.

The release of GDP data for the second quarter is scheduled for Wednesday, Aug. 31. Economists forecast growth of 3.4% for the nation's economy, on par with the prior period.

Traders trying to get a final week of relaxation in before the fall season may want to keep their cell phones handy on Thursday, as some potentially market-moving data will be reported leading up to Friday's all-important jobs number.

Auto and truck sales for August are on tap, with analysts expecting significant declines in both numbers on account of July's blowout sales. But construction spending for July is expected to rise by 0.4%, up from a 0.3% decline in June.

The August ISM Index and personal income and spending data will be released on Thursday, and some economists say this information is on par with the jobs report in offering clues to the Fed's next move. Economists have penciled in 57 for the ISM, up from 56.6 in July. Historically, the Fed has stopped raising rates when the ISM reading drops below 50.

Personal income for July is expected to rise 0.5%, flat with the prior month, while economists anticipate a rise in personal spending of 1% from 0.8% in June.

"With a Fed meeting coming up on Sept. 20, that heightens the importance of these numbers," says John Silvia, chief economist at Wachovia. "We need to see incomes and spending strengthening so people will have confidence in the sustainability of the recovery. There have been big upward revisions in this number over the past few months, so we need to see this continue."

As big as all of these numbers are, they still are just a prelude to Friday's all-important jobs data.

"Once again, it's all about jobs next week," says Rich Yamarone, chief economist at Argus Research. Yamarone is forecasting August nonfarm payrolls to come in lower than the 200,000 consensus estimate as a result of the increasing pace of corporate layoffs.

"We are not creating industrial jobs anymore -- just look at the recent layoffs announced at

Eastman Kodak

( EK) and

Hewlett-Packard

(HPQ) - Get Report

," says Yamarone. "We are reaching the point where these jobs are not being picked up on the service side."

Economists predict the unemployment rate will remain at 5%.

In terms of individual stocks, the U.S. earnings period is well over, but some big-name foreign companies and a few tech stragglers are scheduled to report quarterly results next week.

On Monday,

China Eastern Airlines

(CEA) - Get Report

and

China Southern Airlines

(ZNH) - Get Report

will release quarterly earnings.

The market will hear from

Semtech

(SMTC) - Get Report

and

VA Software

( LNUX) on Tuesday, and

Ciena

(CIEN) - Get Report

on Thursday.