Catching the (short)wave. Americans are joining millions around the globe who listen to shortwave radio

From news to game shows If ``Dallas'' is wearing thin and you're beginning to pick out the villain in ``Murder, She Wrote'' by the first commercial, it may be time to explore another world of entertainment and information found on shortwave radio.

Some 161 countries air programs ranging from news and propaganda to drama and music on groups of frequencies that lie between the high end of the AM - or medium wave - radio dial and the low end of the TV dial.

And while the shortwave region also carries amateur (ham) radio, citizens band, military, ship-to-shore, aircraft, and other forms of communication, international broadcasting is clearly the biggest attraction.

The venerable World Service of the British Broadcasting Corporation (BBC) claims that some 100 million adults worldwide tune in a least once a week. Estimates of its United States listenership range from 500,000 to 2 million people.

The Voice of America, run by the US government, claims a global audience of about 120 million.

A perusal of the BBC program guide ``London Calling'' gives a taste of the variety to be found: news and current-affairs programs, music from rock to classical, drama, game shows, religious programs, books read aloud, listening tips for shortwave buffs, and even language lessons for people who want to learn English.

Listeners fall into three broad groups, says Lawrence Magne, editor in chief of Radio Database International, a publication that lists stations, with their operating frequencies and times, and evaluates shortwave receivers.

``There is the traditional international broadcasting audience - expatriates and people living in countries with poor or censored press,'' he says. He points out that the French, British, and Belgian shortwave services got their start as links between their colonies and the mother country. (The BBC's World Service began in 1932 as the Empire Service.)

The second group lives in the tropics, where countries use shortwave instead of medium-wave frequencies for local programs because of heavy thunderstorm activity. Static from lightning is less disruptive to shortwave signals.

The third group is ``a new type of listener that has surfaced almost unnoticed,'' Mr. Magne says. Many of these people, he says, are ``inundated with new technology'' and are beginning to judge it not by its status value but by what it can do.

Shortwave - what he calls ``world-band radio'' - gives these people more sources of news and allows them to ``travel instantly to various parts of the world.''

The number of shortwave broadcasters has been growing, especially when illegal ``pirate'' stations and those run by ``liberation'' groups are counted. In the US, the number of nongovernment stations has roughly doubled since 1980 to between eight and 10, says Charles H. Breig, chief of the Federal Communications Commission's (FCC) international notifications group. Most of these broadcast religious programs.

One US station, WRNO in New Orleans, may be a harbinger of things to come. Started in 1980, it was the first commercial US shortwave station licensed since World War II, Mr. Breig says.

Last year, something unusual happened. The station ``started showing up in listening diaries across the country,'' says a spokeswoman for the Arbitron rating service. She adds that this is the first time anyone at Arbitron can remember listeners mentioning a shortwave station.

Lawrence Magne suggests that this is an indication that for US listeners, shortwave may be working its way into the mainstream. Getting from here to there

Shortwave programming isn't quite as easy to tune in as your local AM or FM station. And therein lies a key difference between shortwave and the broadcasts most Americans are used to hearing. AM and FM provide consistently strong signals, but only over fairly short distances.

Because it hugs the ground, the most reliable part of a typical AM signal is good out to about 100 miles during the day, depending on terrain. FM is generally good only for line-of-sight communications.

Shortwave signals use frequencies that are very effective at bouncing off the ionosphere, a high-altitude section of the atmosphere. This trait makes long-distance radio communications possible. But it also leaves such communication at the mercy of the sun. Solar radiation affects the ionosphere's ability to return shortwave signals to a given location: Up to a point, the greater the ultraviolet radiation coming from the sun, the better the ionosphere returns radio signals, especially at higher frequencies. Too much solar activity can disturb the ionosphere and Earth's magnetic field, silencing long-distance radio communications.

As result, a listener's ability to pull in a shortwave station depends on the frequency used, time of day, season of the year, and the amount of sunspot activity. This is why shortwave stations either send their signals on several frequencies simultaneously or hand off programming from one frequency to another as conditions change along the signal's path.

Fortunately, the work figuring out when a particular frequency is worth trying has largely been done by experts, who have reduced that information to fairly straightforward graphs and tables. Still, picking up shortwave signals is ``as much art as science,'' says Mr. Magne. ``Signals are not of local quality, but they are listenable.''

And they've grown more so as transmitting techniques and receiver technology have advanced. Satellites link studios to remote transmitters, which are placed close to the intended reception area. Many receivers now use pushbutton digital tuning instead of less accurate slide-rule dials, allowing listeners to preprogram the frequency to which they want to listen. Politics and signal quality

Whether shortwave stations will become easier to tune in may rely as much on global politics as on technology.

``The basic issue is that the high-frequency bands are tremendously overcrowded,'' says Wilson P. Dizard, senior fellow for international communications at the Center for Strategic and International Studies at Georgetown University in Washington, D.C.

He points to competing demands for the shortwave, or high-frequency, bands. On the one hand, there is what he broadly terms ``propaganda broadcasting,'' in which countries, regardless of ideology, try to put their best face forward. Some 70 countries are broadcasting on shortwave ``in a fairly substantial way,'' he says. The range of frequencies allocated for that purpose is limited, and ``the good ones are even more limited,'' he says.

Any attempt to expand the shortwave broadcasting bands to accommodate more stations would come at the expense of other uses. For example, in developing countries, ``shortwave has some very important uses in telecommunications,'' such as telephone service between cities, Mr. Dizard says.

Trying to regulate the shortwave bands is ``a seat-of-the-pants kind of thing,'' says Charles Breig of the FCC.

The International Telecommunications Union (ITU) in Geneva is charged, among other things, with serving as a clearinghouse for information on shortwave frequencies. Four times a year, governments send the union their proposed broadcasting frequencies. The union looks for obvious conflicts and alerts the affected countries. But it has no enforcement powers. As a result, countries tend to lay claim to more frequencies than they use. As a practical matter, many broadcasters monitor these unused frequencies, and if they don't hear any activity, they move in, says Mr. Breig.

So far, attempts to clean up this system have failed. That failure is crucial: In 1979, a meeting of the World Administrative Radio Conference in Geneva set aside new frequencies for shortwave broadcasting, but the conference stipulated that the new frequencies can be used only after the ITU gets the allocation system organized.

Until that happens, there are few options for cutting interference. One widely discussed method is in effect to chop the signal in half by using single-sideband transmitting techniques. But industry observers say the widespread use of this technology for international broadcasting is 10 to 20 years off. Why listen? It's armchair travel

It's the armchair-travel aspect of shortwave radio that has kept Terry Colgan's interest. Mr. Colgan, an Austin, Texas, businessman, says he's been listening to shortwave since 1959, and ``it still amazes me that I can sit in my living room and listen to a radio station in South Africa or Sweden.'' A self-proclaimed fan of National Geographic magazine, Colgan adds that ``shortwave gives me the opportunity to hear the countries I read about.''

While programs on shortwave are as varied as the countries that broadcast them, Colgan and other enthusiasts agree that the BBC's World Service eclipses them all.

``The BBC is the standard against which every shortwave broadcaster is compared,'' Colgan says, citing its ease of reception and standard of announcers and programming.

THERE is a simple rule if you want to try your hand at listening to international shortwave broadcasts: Start cheap.

The number of high-quality receivers has grown in the past 10 years from one to about 50. Prices range from about $70 to more than $7,000.

The radios at the lower end of that range are largely designed to pick up international shortwave broadcast bands, as well as AM and FM frequencies. The higher-priced sets tend to fall into the general-coverage class, capable of pulling in amateur (ham) radio, ship-to-shore, aircraft communications, and other services sandwiched between the international broadcast bands.

The reason for starting off small, says Terry Colgan, special-projects manager for the Association of North American Radio Clubs, is that many people ``don't know anything about shortwave radios. They think that finding a station is easy and that signals are as strong as the ones you find on AM and FM.''

Start with an inexpensive radio that can pick up the stronger services, such as the British Broadcasting Corporation, Radio Moscow, or West Germany's Deutsche Welle, in addition to normal AM and FM frequencies.

``There's no use in dropping a bundle and then finding out you're not interested,'' he says. With a less expensive set, at least you'll still have a reasonably priced AM/FM radio if you find that shortwave listening isn't for you.

If your interest grows beyond the casual, then it's time to look for a higher-priced receiver that will let you pull in weaker stations. Two sources of information are the World Radio and TV Handbook and the Radio Database International. Both have chapters that rate shortwave radios, in addition to exhaustive listings of shortwave broadcast stations, times, and frequencies.

Here is a cursory list of stations that beam English language broadcasts to North America. For additional information about programs, write for sample program guides to the address listed. The times and frequencies are subject to change.