A decade after the communist takeover, Laos is a country dominated by Vietnam and heavily dependent on Soviet Bloc aid, remaining one of the poorest nations in the world.

The Southeast Asian country marked its 10th anniversary of communist rule yesterday, with a parade through the capital of Vientiane and a speech by Prime Minister and communist party leader Kaysone Phomvihan who called for talks between the Indochinese states and their noncommunist neighbors to rid the region of "external interference," according to news reports here.

But 10 years after the communist faction in a Laotian coalition government ousted its U.S.-supported partners and allied itself with Vietnam and Cambodia, Laos is hardly free of external interference.

According to western diplomats and Thai military sources, Vietnam maintains about 50,000 troops in Laos, some of whom are used to help fight insurgent groups of hill tribesmen. In addition, said a senior Thai officer, the Soviet Union has about 500 military advisers assigned to the country.

Foreign aid amounts to about $100 million a year, with Soviet Bloc countries supplying about half of it. Laos has a per capita income estimated at less than $150 a year, making it one of the world's poorest countries.

Unlike celebrations staged in neighboring Vietnam in April to mark the 10th anniversary of the communist victory over the U.S.-backed government in Saigon, the Laotian festivities were low-key. Only a few western reporters were allowed into the reclusive, landlocked country for the event, and dignitaries from other communist states provided the principal audience for the celebration marked by a flyby of Air Force planes and a parade of elephants.

Since the communist takeover there has been a "leveling of income -- all downward," said a western diplomat recently assigned in Vientiane.

"In the old days there was a middle class," but it has largely disappeared under the communists. "Now, having a bowl of noodles in the market is a real luxury" for Laotians, the diplomat said.

Much of the relative prosperity during the Vietnam War era was undoubtedly due to massive U.S. aid as the Central Intelligence Agency organized and funded a secret army, largely made up of Hmong hill tribesmen, to fight the Pathet Lao communist insurgents and their Vietnamese allies.

The Pathet Lao eventually fought their way to a compromise in which they joined a coalition government in 1973. They soon came to dominate it, and by December 1975 were able to abolish the Laotian monarchy, declare a Democratic People's Republic of Laos and send tens of thousands of suspected opponents to reeducation camps.

Today, according to the human rights organization Amnesty International, about 6,000 to 7,000 persons linked to the previous government are believed to be interned without charge or trial in high-security camps or restricted to economic project sites or villages in remote areas.

Amnesty International said in November that the Laotian government had ignored repeated appeals to end the reeducation process now in its 10th year. There was no response to the latest request urging positive action to coincide with yesterday's celebrations.

Since the communist takeover, resistance has been steadily beaten down and now no longer represents a serious threat to the government, according to Thai and western sources. Resistance groups, mainly hill tribesmen, are notoriously fragmented, and many opponents of the government have fled the country.

Thousands of Hmong have streamed from their remote mountain villages after attacks in which they said Vietnamese and Laotian forces used chemical weapons known as "yellow rain."

Since 1975, according to refugee officials, about 315,000 people, or nearly 10 percent of the population, have fled Laos. About 96,000 refugees from Laos remain in five camps on the Thai side of the Mekong River.

Perhaps a greater threat to the Laotian government than the armed resistance is what Prime Minister Kaysone has called a continuing internal struggle between socialism and capitalism. In a January 1985 speech, he said this struggle had "developed to a new phase in a fiercer and uncompromising manner."

Opponents of socialism, Kaysone said, were trying to destroy the communist regime "internally, like a house being eaten by white ants."

Since 1983, more than 100 government officials reportedly have been arrested, according to Amnesty International. Many were charged with corruption, but at least some were believed to have been detained for political reasons.

Despite the country's position as a virtual Vietnamese satellite, relations between Laos and the United States have been improving. This has been largely the result of Laotian cooperation this year on resolving the issue of American servicemen still missing from the Vietnam War.

In February, Laos for the first time permitted a U.S. team to excavate a U.S. airplane crash site with Laotian specialists, resulting in the recovery of the remains of 13 American airmen. A second joint excavation in Laos is tentatively planned for early next year. At present, 556 Americans are still unaccounted for in Laos since the Vietnam War.