AT least 10 people were killed in an outbreak of rioting by soldiers in Zaire's capital, witnesses said on Sept. 24.About 250 French troops were sent to Zaire from bases in the Central African Republic and Chad to protect foreign residents, official sources in Paris said. Two companies of French troops took up positions at Kinshasa-Ndjili International Airport and around the French ambassador's residence with the agreement of President Mobutu Sese Seko's government. Belgian Radio said that Brussels also was sending 2,500 paratroops to protect its 10,000 nationals in its former colony. The looting and rioting began on Sept. 23 when soldiers took to the streets to protest a missed pay rise. Witnesses in Kinshasa said that looters' targets included expatriates' houses and the home of Isaac Kalonji Mutumbayi, president of Zaire's national conference, which has urged democratic reforms under Mr. Mobutu's rule. Zairean opposition parties say the looting is linked to frustration over the slow pace of the conference, which has met only a few days since being convened Aug. 7. Zaire has been in a state of chaos since April 1990, when Mobutu announced a return to multiparty politics. The economy has plummeted due to low world prices for copper and cobalt.