Spreading signs of resistance and popular anger directed at the autocratic rule of President Mobutu Sese Seko are increasing apprehension within the Western diplomatic community about the future of U.S. influence in this strategic and mineral-rich central African country.

The American government's close identification with the apparently shaky one-man rule of Mobutu has made U.S. interests hostage to his fate, American diplomats grudgingly concede.

They have been obliged to report back to Washington that in the past five weeks Mobutu's troops have rounded up several thousand unemployed youths in Kinshasa's slums in a wide-ranging security operation that reflects Mobutu's mounting insecurity.

But the sweep of the youths, who are seen as the potential shock troops of any civilian uprising against Mobutu, quickly degenerated "into a shakedown operation by the soldiers," said one diplomatic source in Washington with access to the reports.

This apparently self-defeating operation, which has increased rather than reduced tensions, illustrates perhaps the most serious problem facing Mobutu -- he is dependent on the military to stay in power, but that military, despite extensive support from outside powers, is an uncertain base of support.

Ironically, the Reagan administration is formulating plans to seek a higher profile here in a period when the situation is becoming increasingly edgy.

Mobutu called on the Army to put down rumblings of discontent in August as well, ordering the major government buildings in downtown Kinshasa surrounded by the French-trained Zairean paratroops of the 31st Brigade. American diplomats here saw this as an extravagent display of force. It went on for several weeks.

Such displays of force have come against a background of economic troubles for this potentially prosperous country. In June, a 67 percent devaluation of the country's currency boosted inflation temporarily from 55 percent annually to 85 percent, while wages remained static. The vast majority of Zaire's 28 million citizens already exist on a bare subsistence level.

But Zaire's former vice premier Bomboko Lokumba, who was recently ousted from the cabinet in one of Mobutu's frequent government shakeups, insisted, "There is no insecurity in Zaire. We are only testing the troops for their quality."

The government moved in the troops in August shortly after someone slipped past Mobutu's personal security and stole from his presidential office a treasured walking stick, a leopard-skin cap and the Army uniform he wore during fighting in southern Zaire's Shaba Province in 1978. While numerous reliable sources confirm the theft, no suspect has yet been caught.

Another disconcerting event for Mobutu was the flight to exile in Belgium of former Zairian prime minister Nguza Karl-i-Bond. Before leaving in April, Nguza had been the Western governments' hope for Zaire developing a democratic government with less corruption. Since publicly calling for Mobutu's overthrow in Brussels and Washington, Nguza has lost the open support he once received from U.S. and Western European governments, who see their interests better served by the current government.

Western analysts and even one of Mobutu's advisers believe that an upheaval is a daily possibility here. "It would only take a spark, I agree," the adviser said.

In the face of this situation, Belgium, the former colonial power here, and France have indicated they want to put more distance between Mobutu and themselves. But the Reagan administration is asking congressional approval of "a substantial increase" in what had been declining U.S. military assistance for Zaire.

In Washington, one State Department official, who has been intimately involved in U.S. policy toward Zaire, confirmed the Reagan administration's desire "to significantly increase military aid" to Mobutu.

"It is one of the few tools we have to exercise any leverage with the Zairians to get them to reform their government," he said.

The administration's recent request for $10.5 million in military aid to Zaire for fiscal 1982 passed the Senate intact. But it was slashed to $4 million by the House subcommittee on Africa.

"The request hasn't gone through the entire legislative process yet, and we think we can get it back up to at least $6 million," the State Department official said.

Since 1977, U.S. military aid to Zaire fell from $27 million to $6.1 million because of congressionally mandated cuts.

The United States has been seen as Mobutu's major supporter since he came to power in a Nov. 24, 1965, Army coup that was partly planned and fully sponsored by the Central Intelligence Agency.

Nine east, central and southern African countries, which run the ideological spectrum from Marxist civilian governments to right-wing military rule, share borders with Zaire, a country of 905,000 square miles, about the size of the United States east of the Mississippi.

The Reagan administration considers Zaire of "central strategic importance" to U.S. foreign policy objectives in Africa, U.S. officials say.

Mobutu has always been able to play Zaire's "strategic card" in getting successive American, French and Belgian governments to ignore his government's brutality and respond to its needs. An argument that Western officials here repeat frequently is that without Mobutu at the helm, Zaire would quickly degenerate into the chaos that so characterized its first five years of independence.

A Zaire in turmoil could destabilize the entire region, and U.S. officials have expressed fears that would give the Soviet Union an opportunity for political exploitation.

Moreover, a stable Zaire is of interest to the United States because of its strategic minerals. The United States buys 60 percent of Zaire's annual cobalt production. Cobalt is a major ingredient for making high-durability alloys used in the aerospace industry.

Yet France's new Socialist government under President Francois Mitterrand and recent Belgian governments have indicated a desire for more distance from the proud and easily offended despot.

Since assuming office in May, Mitterrand has shown his displeasure with Mobutu by changing the venue for the just concluded annual Frano-African summit from Zaire to France. He has also been slow in inviting Mobutu for a private meeting in Paris -- even after receiving many less important heads of state from French-speaking Africa, plus Jose dos Santos, the leader of Angola, a former Portuguese colony. Finally Mobutu was told he would be invited to the Elysee soon.

But Mitterrand did promise to live up to France's commitment to train, equip, maintain and command Zaire's 31st Paratroop Brigade. It remains unclear, however, whether he would commit French troops, as Mitterrand's predecessor Valery Giscard d'Estaing did, to defend Mobutu if unrest develops again in Shaba.

The Belgians, ambiguous about Mobutu and their former colony since Zaire nationalized Belgian mine holdings in 1970, have trained the 21st Infantry Brigade currently stationed around the mining center of Kolwezi in southern Zaire's Shaba Province, but they have refused to equip it. The Zairian government cannot afford to equip it.

Belgium has indicated that it would only send troops to Zaire to help evacuate an estimated 30,000 Belgain nationals. Several thousand French citizens and about 1,000 Americans also live in Zaire.

It is highly unlikely that American soldiers would be sent into Zaire during any crisis to shore up Mobutu's government, but an American administration would likely once again provide logistical aircraft support for any group of soldiers sent to intervene in Mobutu's defense. That was done for Moroccan troops and then French paratroopers when exiled Katangan successionists, now living in Angola, invaded Shaba Province in 1977 and 1978.

The Chinese have just completed training of the first of three battalions of Zaire's new 41st Counterinsurgency Commando brigade.

But even with the newly trained brigades, "Zaire is still easily susceptible to subversion," said one military observer. "There is a lot of discontent here and these units would be largely ineffective against any determined guerrilla threat."

Overall, Mobutu also has allowed his 30,000-member Army to degenerate into a uniformed rabble that is called upon to crush demonstrations by unarmed civilians.

"Mobutu may not want a truly professional Army as it may become a threat to his hold on power," said the source. "After all, Mobutu knows he came to power" in an Army coup.

Army officers routinely pocket their troops' pay and siphon off their food supplies to sell on the black market. The soldiers, in turn, extort money at gunpoint from civilians and set up rural roadblocks to confiscate farmers' produce being transported to markets.

The weakness of the military was demonstrated during two invasions of Zaire's economically vital Shaba Province from neighboring Angola by a force of several hundred exiled Katangans in 1977 and 1978.

As his Army proved incapable of repelling the smaller force, which was reportedly welcomed by Shaba's population, Mobutu had to call on Washington, Paris and Brussels for military assistance in order to save his government.

The conservative African countries of Morocco, Senegal, Ivory Coast, Togo and Gabon also helped Mobutu with soldiers.

Respected political analysts predict that any major upheaval in Zaire would probably be directed primarily against foreign interests and then against the small Zairian political-business elite clustered around Mobutu before fracturing along self-devouring lines of tribal conflicts.

Zaire's population is broken up into more than 200 ethnic groups, and Mobutu, taking a page from Belgian colonialism, keeps them mutually antagonistic in order to help maintain control.

Any organized opposition in the past has been brutally crushed, forcing most of the government's prominent opponents to flee to Brussels and Paris. The exiled opposition to Mobutu had been splintered and ineffectual until recently, affected by tribal differences and the effective suborning of much of its leadership by Zairian government agents.

Mobutu even makes sure that none of his inner circle builds any following by frequent cabinet shakeups. He has reshuffled his cabinet more than 20 times during the 16 years of his rule, most recently in October.

Probably the most open manifestation of growing opposition to Mobutu came late last year when 13 National Assembly members signed and circulated an open letter highly critical of Mobutu's government and containing detailed accusations of corruption, economic mismanagement and violation of human rights.

Despite massive arrests starting in April by Mobutu's security forces -- some of whom were selling copies of the letter they had confiscated for $300 apiece -- for possession of the document, the letter moves around Kinshasa today quite easily.

Yet the challengers were punished with a simple "banning order" to their home districts for five years by a government known to allow lesser political dissidents to be beaten, tortured or killed in prison.

When the banished men returned home they were greeted as heroes.

Any open government opponent still risks brutal retribution and the country's prisons are filled with hundreds of political prisoners who often are beaten, tortured and killed, a Western analyst who monitors human rights here said.

Amnesty International released a blistering public report on the conditions in Zaire's jails a year ago. In July, hundreds of political prisoners were released when Mobutu opened up the prisons to an inspection tour of officials from the human rights organization and the International Red Cross.

"The jails are full again," said the Western analyst, "and there has been a proliferation of secret prisons."