By Kate Gibson

U.S. stock investors have found reason for cheer in recent data showing strength in home and car sales. But analysts caution both markets have drawn only short-lived boosts from government stimulus programs -- one of which ends Monday, the other at the end of November.

"The recent strength in home and car sales got a large boost from the transitory stimulus programs, and we worry that sales have been brought forward," said William O'Donnell, an analyst at RBS, in emailed comments. "If Peter has in fact stolen from Paul, then some benchmark economic releases could look soggier as we hurtle toward year-end."

On Monday, stocks lost hold of early gains to end mostly in the red after a four-day winning streak, with auto-related stocks leading declines among the consumer discretionary sector, which fell the most among the S&P 500 Index's (SPX) 10 industry groups.

Shares of Harman International Industries Inc. (HAR) fell 5.5%. The Stamford, Conn.-based company's core business is the sale of audio equipment to the auto industry. Also hard hit, Goodyear Tire & Rubber Co. (GT) dropped 5.4%.

The Dow Jones Industrial Average (DJI) added 3.32 points to 9,509.28. The S&P 500 Index declined less than 1 point to end at 1,025.57, while the Nasdaq Composite (RIXF) shed 2.92 points to 2,017.98.

Housing- and car-sales data "continue to be skewed by government bailout efforts," said Paul Nolte, director of investments at Hinsdale Associates, in a note.

"What makes the data more concerning for the long-term viability of any recovery that we may be in the middle of is much of the [housing] activity came from distressed sales, inventories of unsold homes still rose, and home prices are still falling," said Nolte.

With the government's "cash for clunkers" program ending late Monday, "we'll now get to see what the natural supply and demand dynamic is in the auto industry," wrote Peter Boockvar, equity strategist at Miller Tabak & Co. .

Shares of Toyota Motor Corp. (TM) slipped 0.7%. The auto maker's Corolla was the top-selling model under the U.S. incentive program. Shares of Honda Motor Co. (HMC), which makes the Civic, the second-best-selling car under the program, tilted 0.1% lower, while Ford Motor Co.'s (F) Focus ranked third. Shares of Ford fell 4.3%.

T.J. Marta, chief market strategist at Marta on the Markets, said that while the "clunkers" program boosted sales and production, the gains came at least partly at the expense of future sales and production, both of which Marta said he expects to see fall "below even recent rates" in several months.

"The program interrupted the much-needed reallocation, or creative destruction, of excess capacity in the auto industry," said Marta in emailed comments.

And, the program prompted "lower-middle- and middle-class owners of older vehicles to lever up on debt and depreciate assets at a time when these people should be shoring up their balance sheets in the face of rising unemployment," the analyst added.

"The other major program, the 'cash for shelter' plan providing tax credits for home purchases, runs to Nov. 30, but there is already talk of enlarging its size and making it available to all home buyers, not just first-time," said Miller Tabak's Boockvar.

In a related note, Jeffrey Saut, an analyst at Raymond James & Associates, said autos and housing have typically been the engines that have pulled the economy out of past recessions.

But, since both are debt-driven sectors, Saut finds it difficult to envision them leading the charge this time around "given the consumer's current de-leveraging mindset," he said.

"The persistent rise in the stock market may be signaling an end to the recession, or investors may be whistling past the graveyard," said Nolte of the market's trend upward.