Ol' king coal -- soon to be recrowned in the US?

Is the world growing warmer? Are sea levels rising? Are polar ice caps melting? Those are just some spinoff questions in a startling survey of America's ''new coal age.''

It is put together by congressional economists who insist that the coal age is just round the corner. In fact, they hold that it's here already and just waiting for the current recession to pass before it starts taking over.

The world is running out of oil, they say. There are 3 trillion tons of coal reserves in the United States. Just the other day freighters lined the harbor at Hampton Roads, Va., to take coal away. And as soon as the present worldwide industrial recession clears up, America stands ready to ''build an energy bridge to the next century.'' According to a summary report made to the Joint Economic Committee of Congress headed by Rep. Henry S. Reuss (D) of Wisconsin, almost unbelievable changes lie immediately ahead. The report comes from the committee's executive director, James K. Galbraith.

Though most Americans don't realize it, the US holds about 30 percent of the world's economically recoverable coal reserves. As global reserves of oil fade, coal must move in. By one estimate, world's coal use will double by 1990 - and triple by 2000.

What kind of a world will it be? The drab prose of the report makes spectacular estimates. America's power stations have been turned from coal to oil, now they may go back to coal again. Much US coal is in Western states, or owned by the federal government. It may be mixed with water and pumped to utility plants in a slurry pipeline. One such pipeline 273 miles long runs from Arizona to Nevada. A proposed new ''coalstream pipeline'' would be 1,500 miles from southern Illinois, W.Va., and on to Florida.

''The US has the opportunity to be what some have called the 'swing' exporter of coal, given its present and expected future capacity,'' the report says. It quotes an international survey from 1980 (''The World Coal Study'') that global coal consumption will multiply three times by 2000.

Says the Reuss-Galbraith report, ''a revitalized coal industry could prove a catalyst for American reindustrialization. . . . The development of a major coal export industry could create in itself a great number of new jobs in the United States as well as offset our trade deficits with countries such as Japan. Finally, such an industry is important for the sake of the security of our allies. . . .''

There is a dark side to the futuristic picture. Increased use of fossil fuel means environmental problems like acid precipitation and the release of carbon dioxide gas that could affect world climate. Some observers think these changes have begun. The present report declares governmental observation is vital. One problem is the so-called ''greenhouse'' effect associated with excessive emission of carbon dioxide into the atmosphere.

According to one team of experts, this has already created a global warming effect. By one forecast, mean global temperature will increase by 1 to 4.5 degrees C. by the end of the century. Another team believes that the greenhouse effect has melted more than 10,000 cubic miles of polar ice in Antarctica. This in turn, they postulate, has caused the water level of the oceans to rise by more than ''four inches since 1940, triple the rate of the previous 50 years.''