After years of isolation, West Africa's firebrand orator of pan-African socialist revolution, Ahmed Sekou Toure, has loosened his grip on Guinea and gradually allowed the country's return to the world community.

But the preceding two decades of Stalinist-like terror remain a dark memory among numerous Guineans.

Toure's socialist People's Revolutionary Republic of Guinea, a West African nation about the size of Oregon with rich mineral and agricultural potential, is today a country of somber paradoxes of poverty and neglect.

In the run-down, decaying capital of Conakry, malnourished children, bloated stomachs bulging from spindly limbs, can be seen being washed by their mothers around the few single-spigot, colonial-era water fountains that work. A mother of five children, with a husband and four live-in relatives to feed, said with despair one day last month in front of a stranger that the family was forced to buy its staple of rice at the black-market price--four times higher than normal. For the first five weeks of this year, Conakry's government stores did not have rice.

Yet in downtown Conakry, opposite mildew-discolored government office buildings, is the multimillion-dollar conference center being constructed for the scheduled summit of the Organization of African Unity this summer. The meeting might not be held because of bitter political controversies in the continent-wide organization.

That Toure, 60, is willing to host an OAU summit with its hundreds of African delegates of wide-ranging political persuasion is a significant measure of how far Guinea's "Supreme Guide of the Revolution" has come from his closed-door policy of the recent past.

A part of his opening-up has included Toure's effort to steadily distance Guinea from its former client relationship with the Soviet Union. According to senior western diplomats here, Toure believes that the Soviets have taken economic advantage of Guinea through fishing and bauxite extraction contracts.

But Toure refused to answer a question about the souring of relations between the two countries on a written questionnaire he required to be submitted before an interview.

The combination of Toure's brand of socialist revolution--which is based on his theory of the need to uplift humankind intellectually, culturally and morally into a "new man"--failed theories of economic development and two decades of heavy military support but meager development aid from the Soviet Union has produced little of tangible measure in Guinea in almost 25 years of independence. Guinea is now listed by the World Bank as one of the world's 28 poorest countries. Much of the rest of Africa, including even the poorest countries, at the same time has moved ahead in various areas of social and economic development.

Politically, Guinea's domestic policies are much like other African autocratic governments and depend on obligatory mass membership in one political party. Few of Guinea's 6 million people escape some official function with the Democratic Party of Guinea.

Guinea's economic problems have been compounded by its low agricultural production, substantial "black market" trading in its overvalued, nonconvertible currency and a pervasive corruption that infuses each level of society.

With the opening of Guinea during recent years, Toure simultaneously began mending his political fences with the West and openly courting the western businessmen, whom he so ardently denounced in past years, to invest in his country as a fifty-fifty partner with his government. Union Texas, an American oil company that has been exploring offshore oil deposits in Guinean waters for several years, has agreed to that arrangement and is scheduled to begin its first drilling operation in the spring.

Another sign of the change was the reception fit for a head of state given to Chase Manhattan Bank's David Rockefeller when he visited Conakry a year ago. Rockefeller reciprocated by assembling corporate officials of 80 U.S. companies for an investment seminar the Guinean leader addressed in New York last summer before visiting Washington for a meeting with President Reagan.

Diplomatic sources said nothing has yet materialized from that meeting for investments in Guinea's numerous mineral deposits of gold, uranium, copper, cobalt and manganese, among some of the minerals here. Since 1973 an American-led business consortium has been extracting bauxite from Guinea.

Toure's name became synonymous with black Africa's anticolonial struggle in 1958 when he convinced his fellow Guineans to overwhelmingly reject French president Charles de Gaulle's offer of an economic-political community of the French colonies led by Paris. Toure campaigned in Guinea against the proposal after de Gaulle reportedly rejected his counter-suggestion of a federation of equals.

In reaction, and as a warning to other French-speaking territories, the French pulled out of Guinea over a two-month period, taking everything they could with them. They unscrewed lightbulbs, took the sewerage pipeline plans for Conakry and even burned medicines rather than leave them for the Guineans, according to Mohammed Damantang Camara, press officer for the Guinean Ministry of Foreign Affairs. Camara said that procedure was followed in all of Conakry's pharmacies and hospitals by the French before they left.

A year before the climatic referendum, Toure had established himself as the undisputed leader of Guinea when his Democratic Party of Guinea, with a militant trade unionist and national peasant constituency, decisively defeated two ethnic-based, elite political parties in elections by capturing 57 of the 60 seats in the territorial assembly.

In his first years of rule, Toure allowed debate, dissent and free speech on government policies.

But a local plot to overthrow him, discovered in 1960, was the beginning of Guinea's long period of government-inspired terror. Matters worsened after a November 1970 invasion force of about 300 soldiers landed in a night assault on Conakry from then Portuguese-controlled Guinea-Bissau. The Portuguese Army-directed troops, half of them ex-Guinean soldiers from the French Army whom Toure had refused to allow back into the country years before, failed to topple Toure.

Throughout the 1960s and early 1970s, there were widespread arbitrary arrests and imprisonments at Conakry's infamous army prison at Camp Boiro on the slightest accusation of antigovernment activities. The program was directed by ambitious domestic intelligence police, whose promotions were based on their abilities to uncover dissenters. Toure kept the country under a perpetual state of siege, periodically announcing the uncovered plots and ordering mass roundups of suspects for interrogation.

Gradually, under the guise of numerous plots Toure said were hatched in many countries including France, the United States, the Soviet Union and China, Toure was able to take firm, personal control of the government, violently repressing the mildest dissent and emasculating the trade unions, his own pre-independence power base. Tight control over virtually every aspect of life was developed through a system of "democratic centralism" under which Toure's party established committees and cells, called "local revolutionary powers," extending to every city neighborhood and in all of Guinea's approximately 4,000 villages.

A fifth of Guinea's population is estimated to have fled into exile since Toure took power.

At least 10,000 people have been rounded up at some time since 1970, and 2,800 have "disappeared," according to the London-based human rights organization Amnesty International. "Many are believed dead as a result of execution, torture, deliberate starvation and inhuman prison conditions," the organization reported in October.

After a 1976 assassination attempt, Toure directed a pogrom against the 1 million Fulani, the largest ethnic group in Guinea.

Asked about the Amnesty charges, Toure sidestepped the question in a nonstop, hour-long interview. "Our concept of human rights is far ahead of human rights practices in countries claiming to be civilized," he said.