Most of the nation's businesses emerged unscathed from the first day of the nationwide railroad strike Wednesday, but companies warned of serious factory closures, shortages and financial losses if the railways remain closed.

"If it goes more than a week, we might begin to experience shortages," said Dick Lovell, a spokesman for the Kellogg Co. in Battle Creek, Mich. However, for now at least, the cereal maker is well stocked with grain at its plants.

Railroads haul about 40% of domestic freight and transport most of the nation's automobiles and auto parts, coal, food and chemicals.

The nationwide rail strike could cost the economy as much as $50 million a day initially, according to the Assn. of American Railroads. After two weeks the cost could rise to $637 million a day, with up to 500,000 industrial workers idled.

The first day of the labor-management dispute that paralyzed the rail system provided a few hints of the possible disruptions to come: Some Kentucky coal mines were idled, a parts shortage forced an Indiana Gener;l Motors plant to send workers home early, and thousands of cartons of California citrus were stuck in rail cars that went nowhere.

The stranded oranges and lemons are "not getting any younger," said Laurence Stern, director of transportation for Sunkist Growers.

In California, the state's three major railroads--Santa Fe, Southern Pacific and Union Pacific--ordered all trains sidelined, leaving customers ranging from beer breweries to oil refineries looking for alternative transportation.

The railroads ordered the shutdown as part of an industrywide show of unity after the union representing machinists ordered a selective strike against CSX railroad.

"We are bringing trains into the terminals and then shutting things down," said Michael A. Martin, public affairs manager for Santa Fe Railway.

The paralysis of the rail system has also backed up other forms of transport. Many West Coast ports--from Los Angeles to Seattle--depend on the railroads to move a large chunk of the cargo at those facilities. At the Port of Oakland--the second busiest on the West Coast--about 60% of the arriving cargo leaves by rail.

Operators of the shipping lines and terminals at the Port of Oakland say that after about three or four days, they will begin running out of room. Some time-sensitive cargo can be sent out by truck, but the heavy demand for trucks to make up for the lost rail car space has made that option very expensive.