Railroad carload traffic increased 2.5 percent in January from a dreadful January 1991, but industry marketing executives express guarded optimism that business is in a slow upturn.

Intermodal loadings, not included in carload data, were up 4 percent, largely on the strength of very strong import and export volume.Traffic executives discount the carload improvement from the year-ago month, but when coal and grain loadings are removed from the data and

comparison is made to January 1990, they have more reason to smile. January last year was affected by the start of the Persian Gulf war and a virtual standstill in the domestic economy.

Coal and grain are bulk commodities that account for nearly half of total rail traffic. Weather and price fluctuations can affect the timing of shipments, but they eventually move.

Although they count on the revenue from coal and grain, traffic executives see more significance in data for other commodities.

Drew Robertson, president of Atlantic Systems Inc., a New York consulting firm that provides data for The Journal of Commerce monthly freight review, cites comparisons with two years ago as grounds for his optimism.

"Coal and grain have not reached their 1990 levels, but key commodities such as chemicals, autos and metals are pretty much even," he said.

Movement of containers exceeded trailer loadings in intermodal traffic for the first time since records have been kept. Container traffic increased 14.2 percent to more than 300,000 units in the month, while trailer-on-flatcar traffic fell 5.2 percent to fewer than 280,000 units.

While domestic traffic increasingly moves in containers, the shift last month almost entirely reflects foreign trade.

Henry V. Logan, senior vice president for fleet management at TTX Co., said ships arriving at West Coast ports were essentially full. TTX operates much of the national fleet of intermodal cars for the railroads. It is owned by a group of major carriers.

"Last week, we had zero cars stored serviceable," Mr. Logan said. He pointed out that TTX ordered 1,200 double-stack wells in five-unit combinations last Friday, along with 900 stand-alone units. The order was part of the company's previously announced capital program.

Much of the arriving traffic is believed to be merchandise for the Easter season, one marketing executive said.

"Traffic is holding up pretty well in non-coal, non-grain commodities," said Patrick J. Krick, director of marketing and business analysis at Burlington Northern Railroad Co. "Since things stalled in the fall, there's been no real deterioration in merchandise traffic. There's not really been a decline, but a stoppage of growth since then."

BN carload traffic was up 7 percent in January, aided by heavy volume of grain moving to Pacific Northwest ports for export to Pacific Rim countries. Coal also increased on Burlington Northern.

William E. Voltz;, vice president, merchandise marketing, at Norfolk Southern Corp., is cautiously optimistic about the economy.

"Our paper business was very strong and paper usually leads the economy," he said.

The company's container intermodal business and Triple Crown hybrid road- rail traffic were particularly strong last month.

More than 40 percent of Norfolk Southern traffic is coal, and coal traffic was down in January. William B. Bales, NS vice president for coal and ore traffic, cited mild weather for the decline.

"There was virtually no spot ordering of coal in our territory," he said. ''That left us with base-load business, but we usually can count on utilities buying additional coal."

Aden Adams, CSX Transportation Inc. vice president for merchandise sales and marketing, saw things similarly. CSX coal traffic also is down, as was grain.