Rwanda's military leader, Vice President Paul Kagame, admitted publicly for the first time today that his troops are involved in the Congolese conflict launched three months ago by rebels trying to oust President Laurent Kabila.

After months of official denials, Kagame, who is also Rwanda's defense minister, acknowledged his country's role following an hour-long meeting here with South African President Nelson Mandela, two days after he had met with the U.S. assistant secretary of state for Africa, Susan E. Rice, in Kigali, the Rwandan capital.

Diplomats had described Rwanda's denials as a major obstacle to mediation efforts to end the widening war in Africa's third-largest nation, which has become a continental conflict. The war, which broke out Aug. 2, has drawn in Angola, Zimbabwe, Namibia, Chad and numerous regional militias on Kabila's side, with Rwanda and Uganda supporting the rebels.

"Initially, our country hadn't, for good reasons, come out specifically to talk about the presence of our troops in Congo," Kagame said today, seated beside Mandela at a news conference. "We have informed the president that we are there specifically for our national security. That situation in Congo has always affected our security, and we are there specifically for that purpose."

Rwanda, Congo's neighbor to the east, has involved itself in two Congolese conflicts in the past two years, and in both cases it persisted for several months in denying it. Also in both cases, Rwanda's military moves were intended to combat Rwandan ethnic Hutu extremists, including perpetrators of the slaughter of 500,000 Rwandan Tutsis in 1994, who use Congo as a base for attacks against Rwanda. In the first war, launched in 1996 -- when Congo was called Zaire -- Rwanda led the forces that ousted dictator Mobutu Sese Seko and installed Kabila in power.

Since the outbreak of the latest Congo war, Rwanda again maintained a policy of denial, despite sightings of Rwandan troops inside Congo and confirmation by Congolese rebels that Rwandans were in the conflict. Uganda has admitted it has troops inside Congo, but Rwanda's denials scuppered several attempts at mediation.

"Many people felt that the fact that Rwanda did not admit that they were combatants created immense difficulties" for the peace process, Mandela said. "Now that Rwanda has made this acknowledgment, I think that we have reason to believe there is going to be progress."

The negotiating framework that Mandela and others are proposing includes a cease-fire, a troop standstill, a foreign troop withdrawal and more talks leading to Congolese elections. But Kabila's government said Kagame's statement was not enough for Congo to agree to a cease-fire, the Reuters news agency reported from Kinshasa, the Congolese capital.

"For us, saying that they are there makes no difference because we knew they were there. They must withdraw," said Kabila's chief political aide, Pierre-Victor Mpoyo.

Although thousands of mutinous troops from his own army appear to form the core of the rebel force, Kabila has called the conflict an invasion by Rwanda's ethnic Tutsi-dominated army and its close ally, Uganda. Some diplomats also have characterized the war as an invasion.

Rwanda maintained its silence on its involvement in an effort to avoid fueling "that confusion," Kagame said.

"The conflict was an internal conflict which has brought in external forces," he said.

After helping to install Kabila in power in May 1997, Rwanda allowed hundreds of its troops to remain in Congo to help organize and professionalize Kabila's new military. But Rwanda gradually fell out with Kabila over the issue of border security. As relations became strained, Kabila suddenly announced late in July -- despite prior agreement on a Rwandan withdrawal -- that he was kicking Rwandan troops out of the country. This, coupled with Rwanda's belief that Kabila was recruiting Hutu extremists for his army, led to a final breach.

Kagame was vague today about precisely when his troops moved into Congo. He denied that his army was inside Congolese territory on Aug. 2, but suggested that forces moved in soon after.

With its complex ethnic, economic and nationalistic dimensions, the Congo conflict has alarmed African and Western leaders because of its potential to broaden even further and become more intractable.

"If this conflict is not stopped, the danger of a massive African war is a reality," Aziz Pahad, South Africa's deputy foreign minister, said Thursday.

During her attempt at shuttle diplomacy in several of the combatant states this week, Rice met with Kabila and, in effect, told him, "He can be part of the solution, or he can continue to be part of the problem," a U.S. official said. "And if he continues to stand on his current ground, this place will continue to explode."

Asked how long Kabila can hold out, the official said, "As long as the Angolans and the Zimbabweans are willing to stand by him, I think indefinitely." CAPTION: Rwanda's Kagame was vague about when his troops entered Congo. ec