For the first time in its history, Brazil is finding out what really exists in its mythshrouded Amazon jungle. An accurate profile of this region - which is vast, remote and largely uninhabited, yet potentially rich in natural resources - is beginning to emerge from an ambitious aerial radar survey organized by the Brazilian government.

This undertaking could help Brazil develop the Amazon jungle in a rational and intelligent manner and move the country closer to its goal of becoming a major developed nation.

The aerial survey, which has cost some $25 million in the past six years, has produced an incredible amount of new data about the region. It also has revealed how Brazil wasted large amounts of time and money, both foolishly and destructively, on poorly thought-out Amazon development schemes in the past.

Radar maps produced by the survey indicate that the Brazilian region is dotted with potentially valuable deposits of minerals such as bauxite, iron ore, tin ore, manganese, limestone and even gold, diamonds and radioactive substances - which no one knew were there before. The radar maps show that some of the Amazon's tributaries and mountains - which have been routinely marked in on globes and atlases all over the world for years - actually are miles away from where mapmakers thought they were.

The survey maps also tell which parts of the Amazon jungle may be best suited for farm settlements and highways, which parts should be used for large-scale timber and cattle raising, and which parts or ecological or economic reasons - would best be left alone. Detailed reports accompanying the maps note that much of the development in the region so far has been the wrong kind in the wrong place.

"People have spoken of the Amazon jungle as everything from a green hell to the breadbasket of the world," says Otto Bittencourt Netto, technical director of the project. "But we who have been working there all this time don't dare to make a single affirmative statement about that region yet."

The radar maps are complied from images collected by a Caravelle jet airliner that has been methodically crisscrossing the Amazonian skies at 32,000 feet, at a speed of 530 miles per hour.

The radar information is then checked on the ground by technicians who are lowered into the otherwise inaccessible jungle by Brazilian airforce helicopters. More than 40 people have been killed during the mapping project, most of them in helicopter crashes.

To date, 960,000 square miles of Brazil's Amazon region have been charted with radar maps - comparable to an aerial survey stretching from the tip of Maine to the tip of Florida and extending westward a bit past the Mississippi River.

Some of the survey's findings have been classified by the Brazilian armed forces - such as maps of Brazil's borders with French Guiana, Surinam, Guyana and Venezuela. This could aggravate fears that Brazil harbors imperialistic designs on the rest of the continent, although Brazil insists that it has no dreams of expansion.

Much of the radar survey information is available to the public and some has been distributed overseas. Report No. 10, which was just released, is typical. It covers a rectangular section of jungle measuring 113,500 square miles - equal in size of the state of Arizona - which includes the important cities of Manaus and Santarem, long stretches of the Amazon and Tapajos rivers and a major part of the new and much-ballyhooed Transamazon Highway.

A look at highlights of the report shows the region's potential richness as well as the bad planning and lack of coordination that has occurred there already:

The radar has picked up indications of nearly 25 important minerals in this section, including what appear to be commercially exploitable deposits of bauxite, iron ore, gypsum and rock salt. Several mining companies, foreign as well as Brazilian, are actively interested in starting up projects, the report says.

Large expanses of land beneath the jungle foliage in this section are swampy and "do not offer favorable conditions for the planning and execution of highway projects."

Yet this is precisely where an important part of the multimillion-dollar Transamazon Highway - rushed into construction several years ago during a euphoric period of nationalism - goes through and frequently suffers major washouts.

Much of the soil in the section is, according to Report No. 10, "acidic and of low nutrient content, which seriously limits its productivity." Yet this is where Brazil tried to get millions of homesteaders and small farmers to settle and make new lives. The radar survey explains, in part, why the Amazon homesteading drive flopped.

The aerial survey did detect one large strip of fertile farmland in this section, but the report noted that this and now is being cleared for grazing. This, it predicted, will cause erosion and permanently ruin the land for farming - and possibly bring about the frequently theorized "Amazon desert."

On the other hand, the radar spotted large areas in the section that seem of little use for farming but apparently would sustain cattle ranches. The report said there are no cattle on these lands now.

Many of the tributaries of the Amazon River that run through the section are navigable all year and serve as the cheapest and most efficient means of transportation and commerce in the region, as opposed to highways, the report said. But it added that few of the towns and settlements along these tributaries have bothered to build river ports, docks or even rudimentary stairways for loading and unloading boats.

The Brazilian government now seems willing to try to correct past mistakes. The radar project grew from a minor geologist survey in the Ministry of Mines and Energy because federal officials were impressed with its early work. Now the government has told the project's directors to extend the radar aerial mapping and reporting to the rest of the country.