NEW YORK (CNN/Money) - Consumer spending boomed in the third quarter, driven by tax credit checks, tax cuts and cash from mortgage refinancings.

But the boom was short-lived, and stronger wage growth will be needed to keep spending and the broader economy healthy in 2004, economists said Monday.

Consumer spending rose 0.8 percent in August, the Commerce Department reported Monday, helped along by a 0.9 percent jump in after-tax disposable income, which itself was mainly the result of child tax credit checks and tax cuts, analysts said.

In July and August, consumer spending -- which fuels more than two-thirds of gross domestic product (GDP), the broadest measure of the economy -- grew at a blistering annual pace of 7.6 percent, according to UBS Warburg economists.

But that probably changed dramatically in September, many economists said, driven by an expected sharp decline in automobile sales.

"Certainly, the degree of strength through August is not sustainable; we'll get a much weaker number in September," said UBS Warburg senior economist Jim O'Sullivan. "But the third quarter as a whole will still show 5 to 6 percent consumer spending growth, even if we get a negative number in September."

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Consumer spending grew at a 3.8 percent rate in the second quarter, helping to push GDP up at a 3.3 percent pace. A consumer spending growth rate of 5 to 6 percent will help many analysts' predictions of 5 percent GDP growth in the third quarter become a reality.

But the effects of tax credits and tax cuts are already starting to fade, and a recent jump in mortgage rates has tamped out the refinancing boom, so consumer spending will have to find something else to support it, many economists said.

"The number one problem continues to be a lack of job and income growth," said Wachovia Securities senior economist Mark Vitner.

In Monday's Commerce Department report, wages and salaries grew a paltry 0.1 percent, echoing other data that have shown how a labor market slow to recover from the recession of 2001 has weighed on wage growth in recent years.

Sluggish wage growth hasn't stopped consumers from shopping. CNNfn's Kathleen Hays takes a closer look at consumer spending. Play video (Real or Windows Media)

Payrolls are 2.8 million jobs lighter than they were in March 2001, when the recession began, the longest stretch without job growth since World War II. Meanwhile, wages and salaries grew at just a 1.9 percent pace in the second quarter, according to the government data, a far cry from the 8 percent growth rate in 2000.

"Consumers had a nice July and August. Unfortunately, they're on their own for the fourth quarter, which starts on Wednesday," said Delos Smith, senior economist at the Conference Board, which publishes a monthly survey of consumer confidence. "Going into 2004, spending is going to be based on wage and salary growth, which needs a boost."

Consumer confidence measures have shown weakness in recent months, driven by worries about a sluggish job market. The Conference Board's index for September, due on Tuesday, is expected to show a drop to 80.6 from 81.3 in August, according to economists surveyed by Briefing.com.

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Of course, consumers don't always spend the way they feel. Confidence plunged after the Sept. 11 terror attacks, but consumers were able to rouse themselves to buy new cars.

What's more, there's still some money left from mortgage refinancing, and tax cuts may provide another boost in the first quarter, when people realize their April 15 tax bill is lighter.

"Consumer spending is going to slow down, but it's probably going to grow somewhere in the 2.75 to 3.5 percent range for the next several quarters," said Paul Kasriel, senior economist at Northern Trust.

But that may not be enough to speed up the labor market's recovery.

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Several quarters of reasonably strong economic growth aren't expected to push the unemployment rate much below its current level of 6.1 percent in 2004, and that could keep wage growth static for some time, many economists believe.

"What we're looking for is evidence of the corporate side of the economy gaining confidence and making real commitments in its own spending. There, I'd say the news is at best mixed," said Lehman Brothers chief economist Ethan Harris.

"We are going to get some follow-through, some hiring, but it will be slow. I don't see wage growth coming back in the next year."