Beneath the clattering Aeroflot helicopter, the Siberian forest stretches aimlessly, a frozen empty quarter of moose, bear, elk, reindeer and wolf-but now bearing on its wilderness face the unerringly accurate hand of man.

Everywhere, the dense forest of pine, birch and Siberian larch is criss-crossed with narrow, perfectly straight paths chopped through the trees for miles to the horizon. The paths intersect, run parralled, and perpendicular to each other.

These are the tracks made by Soviet geologists, busy at work with seismic gear sounding out the hidden mysteries of frozen earth below, probing for the truths to be learned of one of the largest natural gas fields on earth.

It is work that has proceeded intensively here for more than a decade in ruthless winters and harsh summers. At stake may be a remarkable scheme to send the gas thousands of miles across the forest through a pipeline still to be built, to a Pacific Ocean port that does not yet exist, and into tankers still to be constructed, to feed the inexhaustible demands of home and industry in Japan and the United States.

Nothing may come of this project, but it is virtually certain that even if every geologist disappeared tomorrow, never to return, our grandchildren would be in their dotage before the taiga-the Siberian forest-ever recovered. For in the brutal climate of eastern Siberia, it takes 60 years for a tree to reach full size.

The odds against the project reaching fruition, even late in the next decade, seem quite high. The proposal has been buffeted by sharp political differences between Moscow and Tokyo, financing hurdles in the United States that are partially political, and complex technical questions of construction, reliability, and safety, including concerns over earthquakes and icebergs.

One certainty in this frontier prospecting settlement of log cabins and a superb guesthouse is the enthusiasm of the geologists for their labors.

The first party of them landed here (Kyzyl-Syr means Red Sands in the Yakutia dialect) in 1965. The settlement now numbers 6,000, including geologists, test-well drillers, laborers and technicians and their families.

The community is served by Aeroflot helicopters and trucks and buses using the frozen Vilyui River, plying equipment, food and people between here and the larger settlement of Vilyuisk about 50 miles downstream on the Vilyui.

Like other Siberian settlements, the winter gives Kyzyl-Syr a snow-mantled, picture-postcard air.

While Aeroflot helicopters roar in and out of the small landing area at the river's frozen edge, pet huskies bark from backyards and tiny moppets bundled in thick winter garments trundle about in the 35-degree-below-zero cold, playing hockey on the packed snow streets, or idly passing time in snowy games while the older children attend school and their parents work or rest.

Life is simple. An otherwise cheerful dormitory manager says: "Life here is dull, dull, dull. The men work four days at a time outside and then come back and rest for four days."

Her unmarried charges live four to a room in the three-year-old, spotlessly clean, wooden two-story dorm.

"When they come back from work, they are too tired for normal social life," she says. "If they don't like television, there's nothing to do." A color TV in the community room receives central Moscow programming via satellite. Moscow TV is heavily laced with political lecturing and classical music and drama.

"The diet is hard for growing children," she says: "No fruit, no fresh vegetables, no fresh milk," right through the eight-month-long winter.

Some grade school children, agog over never-before-seen Americans visiting their isolated community, paused one afternoon for talk.

Of the three, one spoke schoolboy English, and another, rudimentary German.

"How-do-you-do?" singsongs the English speaker. "I am fine." Then, with a broad grin, "Chewing-gum?" He and his mates all had badly discolored teeth that seemed destined for early extraction and replacement with stainless-steel false teeth, another common feature of life in the Soviet Union.

The gas field here is one of three large gas deposits discovered in the Soviet Republic of Yakutia in the past two decades. Geologists have mapped reserves of 200 billion cubic meters here and their discoveries are being proven out by exploratory wells. In all, the Soviets have confirmed the existence of about 800 billion cubic meters of natural gas in three immense fields in the south Yakutia region.

Yuri Pilipenko, chief of the expedition, and Vyachislav Belinken, chief engineer, expressed confidence that by the end of the year, the total will top a trillion cubic meters.

This amount is considered necessary by the Japenses and Americans interested in splitting an estimated $4 billion investment tag. They would be repaid with natural gas.

The major consortium partners would include Armand Hammer's Occidental Petroleum, EL Paso Natural Gas, and Tokyo Gas, the retailing company in the Japenses capital. Talks about the feasibility of the project have continued for a number of years.

Under the proposal, the two countries would supply well-drilling equipment, compressors and pipeline, and in return would be guaranteed deliveries of 10 billion cubic meters of gas annually for 25 years.

The Soviets are confronted with major questions, however.

First, the Yakutia fields are scattered and no economical way to join them in a single massive production unit has been found.

The second problem is to find the cheapest route to the Pacific, and to choose a safe, year-round port, no easy task since much of the Soviet fat east coast is icebound or threatened by icebergs during the winter.

The Soviets have proposed three routes to the coast, but have not seriously begun the surveying of perma-frost zones, seismic zones, and other aspects. A decision on the best route seems some time away, and that would be followed by the massive problem of assembling construction gangs in labor-short Siberia for yet another giant project.

The tankers are another major question. These would be cryogenic ships, carrying the highly volatile gas liquefield in super-cooled form. Port facilities, compression and cooling equipment, demanding high technological competence, must be built and made to work.

The Soviets recently renewed an earlier notion that the port of Magadan in the Sea of Okhotsk would be both the cheapest and safe, but American analysts have expressed concern that icebergs are plentiful there, posing great danger to the ships and their explosive cargos.

For the Soviets, who have 80 percent of their energy resources in Siberia, while 80 percent of their industry is thousands of miles to the west, in the Urals and European Russia, the South Yakutia project seems to hold the only practical way for relatively cheap and fast exploitation of these fields.

With vast new gas supplies now being pumped westward from west Siberian and Central Asian gasfields to markets in the East bloc and Western European countries, the Yakutia fields present a perplexing situation.

Meanwhile, the prospecting and test drilling continues here, and with the aid of two recently purchased American seismic rigs, will increase. The test wells are being capped and marked, and the only gas being pumped is for local consumption by the commuity established to find it in the first place.

Meanwhile the Siberian forest will never be the same. CAPTION: Map, By Richard Furno-The Washington Post