Moscow's helping hand: how dependable?

When a private plane went down in a heavily wooded area near Dawson Creek in northern British Columbia last September, the nearest help was 600 miles away - straight up.

A specially equipped Soviet navigation satellite relayed the plane's emergency locator signal to a receiving station in Ontario 2,500 miles from the crash scene. As a result, rescuers were able to locate the plane and save three lives.

''Based on normal search tactics, the area where the plane went down would not have been searched for another three or four days. It is unlikely they would have survived that long,'' says Capt. Ted Kasprzak, duty controller at the Canadian rescue coordination center in Ontario.

The Soviet satellite COSPAS (a Russian language-derived acronym), launched June 30, is the first entrant in a joint US-Soviet-Canadian-French satellite search-and-rescue effort that will eventually comprise a network of four such orbiters capable of relaying emergency signals from anywhere on the face of the globe.

The first US SARSAT (search and rescue satellite-aided tracking) satellite is scheduled for launch in March 1983, followed by a second Soviet satellite in midsummer, and a second US satellite in the spring of 1984.

The COSPAS/SARSAT project is an outgrowth of the current international emergency locating procedures. By law, all US commercial aircraft and ships, as well as those of many foreign nations, must carry an emergency locator transmitter (ELT) that broadcasts a distress signal when activated. If a plane crashes or a ship flounders, rescue craft can tune into this emergency frequency to locate the vessel in distress.

For various reasons the transmitter's signal cannot not always be received. In some cases it is simply a matter of the distances involved. In the British Columbian incident, the steep mountainous terrain prevented rescue aircraft from picking up the signal.

Enter the satellite. It relays emergency signals to any rescue station within its range and monitoring the rescue frequency. From the signal, rescuers can determine a plane's or ship's general location.

Already there have been four documented rescues since the Soviet satellite was launched - involving two plane crashes in Canada and two boating accidents in the United States in which a total of 12 people were saved. The satellite has been instrumental in locating half a dozen other planes and vessels in which there were no survivors.

The international project took shape shortly after the 1976 Apollo-Soyez space flight. Soviet officials journeyed to Washington to meet with NASA officals and explore additional areas for cooperation in space. The idea for a satellite rescue system was broached at that time and further exploratory meetings took place over the course of the next three years.

In the meantime Canada and France were studying the concept and were eventually brought into the effort. In 1980 representatives of the four countries signed a formal memorandum of understanding. The Soviets were given the specifications and built a system compatible with US standards.

In a period of tense US-Soviet relations and concern over the increasing sophistication of Russian technology, the COSPAS/SARSAT project is drawing praise as a model of both effectiveness and cooperation.

''There hasn't been a single hitch in our relationship with the Soviets,'' says Bernie Trudell, search-and-rescue mission manager at the NASA Goddard Space Flight Center in Maryland. ''It has been a very cooperative venture with a complete absence of political undertones.''

The Russian have provided the coordinates of their orbiting COSPAS satellite, allowing rescuers in this country to pick up emergency signals directly from the orbiter. In fact, the only time the Soviets know their satellite is instrumental in a rescue is when US officials tell them.

And, ''the system is based on an absolute minimum of technology transfer,'' says Mr. Trudell. ''In fact, there was none.''

The Soviets chose to build search-and-rescue capability into their navigation satellites, which are used principally to direct their extensive maritime trade. Their voluminous shipping is the reason the Soviets are cooperating in the search-and-rescue system; they have considerably less commercial air traffic than the US.

Although the area in which a low-orbiting search-and-rescue satellite can detect a rescue signal stretches from one pole to the other, it still leaves certain areas uncovered as it circles the planet. The advent of four satellites will mean that all areas of the globe will be covered all the time.

The US was originally scheduled to launch the first satellite with search-and-rescue capability, but the weather satellite it was designed to replace survived long past its expected lifetime, so scientists delayed the new satellite's launch.

So far the only hitch in the program is the number of false alarms the satellites are receiving. Every time the satellite circles the globe, it records an average of six distress signals. More than 97 percent of the distress signals reported are false alarms. Many are mechanical failures. Because of their current design, an ELT can often be triggered if accidentally dropped.