WASHINGTON (Reuters) - Higher costs for gasoline and food again put pressure on a key gauge of retail inflation in May, according to economists polled by Reuters ahead of Friday's release of the monthly consumer price index.

The Consumer Price Index, the most broadly used gauge of inflation, will likely rise 0.5 percent in May, the biggest monthly gain since November, after a 0.2 percent rise in April, based on the median forecast of 80 economists.

Some of the energy-related costs are working their way into other prices, such as airline tickets as jet fuel costs jump, economists said.

With the erratic food and energy sectors stripped out, the so-called core rate of consumer prices is forecast to rise 0.2 percent following a 0.1 percent rise in April as a weak economy and tight-fisted consumers keep inflation in check.

"Despite moderation of core inflation since the start of the year, inflation expectations have soared as gasoline and food prices have climbed," Wachovia said in its U.S. outlook. "If economic growth remains below trend, as we expect, inflation should trend lower giving some relief to the Fed."

The following is a selection of comments from economists:

GLOBAL INSIGHT

Forecast: CPI +0.6 percent

Core CPI +0.2 percent

A core number higher than 0.2 percent would start to ring alarm bells at the Fed that rising commodity prices are filtering through to core inflation.

JPMORGAN CHASE BANK

Forecast: CPI +0.6 percent

Core CPI +0.2 percent

The key core CPI categories that we expect to be firmer than in the last few months include lodging away from home, medical care and airfares.

LEHMAN BROTHERS

Forecast: CPI +0.5 percent

Core CPI +0.2 percent

We expect owner's equivalent rent, the largest component of the core CPI, to rise by a subdued 0.2 percent, reflecting the housing supply glut. Upward pressure should come from apparel prices and the service components of medical care and education.

RBS GREENWICH CAPITAL

Forecast: CPI +0.6 percent

Core CPI +0.3 percent

We look for hotel rates to rebound. The pattern in this component so far this year has tracked fairly closely with 2003, a period when the travel industry was still reeling from the attacks of September 11 and was hit further by the uncertainty associated with the war with Iraq. The projected pickup in hotel rates, airfares, medical care prices and recreation costs would be enough to produce a 0.3 percent rise in the core.

(Polling by Bangalore Polling Unit)

(Reporting by Nancy Waitz; Editing by Tom Hals)