When American oilman L. Scotty Greenwald talks about his Marxist hosts, he makes this languid river-port capital sound like Abidjan, the busy investment haven of the Ivory Coast.

"They welcome the American technological skills and we've had nothing but excellent cooperation from the Congolese," said Greenwald, the director of the Cities Service Co.'s new operations here. "In less than six months, we've opened two offices."

What Greenwald implied is that this communist country does not fit any easy Third World socialist stereotype. American and European businessmen can do as well with the Congo's pragmatic government, he said, as they have done with Angola's, this country's Marxist neighbor to the south.

Cities Service just recently anchored an oil-drilling platform offshore, becoming the first American company to take part in the Congo's oil boom. The Congolese government wants to diversify the oil interests it deals with so as not to be too dependent on the French and Italian companies now producing here.

Last year American scientists led two expeditions into the Congo jungle looking for remnants of a water-dwelling dinosaur called mokele-mbembe, an elephant-sized creature extinct for 60 million years. Neither expedition found a trace of the legendary beast, but a Congolese rock band produced a song and created a mokele-mbembe dance to honor the efforts. Like the expeditions, the song and dance were flops.

Apart from such light moments, Brazzaville gives an impression of stern, revolutionary Marxism. Amid the tropical greenery of the city's streets are the usual larger-than-life portraits of Marx and Lenin. Everywhere are billboards with such messages as "Seven hours of work and not seven hours at work" and "Be revolutionary to assure the primacy of the general interest above individual interest."

While the domestic scene is calm today, the Congo's road to socialism has had its rocky moments. Several years ago, ideological purists in the government reportedly brought the country to the brink of economic disaster by trying to pull the Congo out of the French-run monetary union. The convertibility of the Congo's franc, like currencies of most French-speaking African nations, is guaranteed by the French treasury.

A trade union upheaval, an Army coup, an assassination and a political party coup have toppled four Congolese governments since the country won independence from France in 1960. The present head of state, dapper Army Col. Denis Sassou-n'Guesso, 39, maintains a delicate political balance among the groups--the Army, the trade unions and intellectual Marxist civilians. But his government could be overthrown as well.

Yet the Congo is not easy to compare to Africa's other socialist countries. Sixty percent of the economy is dominated by flourishing French-owned private commercial and manufacturing interests. The rest of the economy is tied to more than a hundred state-owned businesses. A majority of them are money losers and are a serious drain on the Congolese treasury.

Rising revenues from a four-year, 113 percent jump in oil exports--now about 110,000 barrels a day--are financing a skyscraper building spree in Brazzaville and have led to the commercial rebirth of Pointe Noire, the Congo's Atlantic Ocean port. Per capita income of the 1.5 million people is an astronomical $1,000 a year, by African standards. The government has begun pouring millions of dollars in oil earnings into road building and agricultural development in the Congo's largely untouched forested interior. Last year, civil servants received a 13 percent salary increase, the first in years.

French journalists, who keep a close watch on events here, have labeled the Congolese leadership "Marxist-capitalist," riding a wave of oil-generated prosperity. The Congo enjoys a special place in French nostalgia, because Brazzaville was Charles de Gaulle's headquarters for a time during World War II. It was at Brazzaville that de Gaulle made a speech in 1944 promising to reform France's colonial policies.

Congolese government spokesman Emmanuel Adzou chuckled at the "Marxist-capitalist" label.

"We are not turning toward the road to capitalism," he said. "It has been necessary for us to make a slow transition to socialism because we lack the cadres to accomplish this goal rapidly. We do not want to disrupt the economy overnight."