Rising energy costs probably drove American consumer prices higher last month and may cause the expansion to slow, economists said in advance of reports being issued this week.

The Labor Department’s release on consumer prices is likely to show that they increased 0.2% in September, the biggest gain in three months, after rising 0.1% in August, according to the median estimate of economists surveyed by Bloomberg News. The report comes out in a day.

The index of leading economic indicators, a gauge of the economy’s likely direction, slipped for a fourth month in September, according to the median forecast. The soaring price of oil, combined with weaker job growth than earlier this year, may cause consumers to watch their spending, economists said.

“We expect higher energy prices, sluggish business confidence, and a cooling off in consumption to lower the economy’s 2005 trajectory,” said Joseph Abate, a senior economist at Lehman Brothers Inc. in New York. The economic expansion is about to enter its fourth year.

The consumer price report will probably show energy prices rose 0.6% last month, propelled by higher costs of gasoline, home heating oil, and natural gas, according to Mr. Abate.

Crude oil on the New York Mercantile Exchange rose to a record $55 a barrel Friday. Federal Reserve Chairman Alan Greenspan said the same day that energy costs have had a “noticeable” effect on the economy.

The rise in the value of oil has shaved about three-quarters of a percentage point, or $75 billion, from gross domestic product this year, Mr. Greenspan told the National Italian American Foundation. “The risk of more serious negative consequences would intensify if oil prices were to move materially higher,” he said.

The economy grew at a 3.3% annual rate in the second quarter of this year. A Bloomberg News survey calls for a 4% rate of growth in the third quarter, which ended September 30,followed by 3.8% in the final three months of 2004.

Prices excluding food and energy, a less volatile indicator of inflation, also rose 0.2% in September after rising 0.1% in August, according to the survey median.

Higher costs for services such as medical care, movie admissions, and college tuition, may have pushed up the so-called core rate of inflation, according to Bill Sharp, a senior economist at J.P. Morgan Securities Inc. in New York. Prices of goods, such as new cars and computers, probably fell, he said.

The index of leading economic indicators very likely dropped 0.1% last month after falling 0.3% in August, according to the survey median. The index, which attempts to gauge where the economy is headed in three to six months, began falling in June.

“While the composition and change in the index is a bit disappointing, we do not expect the economy to slip into recession any time soon,” Mr. Abate said. The current expansion started in November 2001, according to the National Bureau of Economic Research, the arbiter of when recessions begin and end.