Pope John Paul II celebrated mass today at the St. Pierre Church here and told the predominantly African congregation of the importance of the monogamous Christian marriage, calling: "The most audacious and marvelous contract that has ever existed."

"In God's design the couple is monogamous . . . This monogamy is not Western but of Semitic origin . . . Each partner is recognized to be of equal value in the totality," the pontiff said in a homily delivered in French.

The pontiff took aim at polygamy, a tradition that has survived in Africa despite opposition from the Roman Catholic Church.

"The tradition of the family is deeply rooted in the African soul," the pontiff said.

The Polish-born pope began his 10-day, six-nation tour on Friday, receiving an exuberant welcome from more than 1 million persons on his arrival from Rome.

John Paul was greeted by a choir and spear-brandishing tribal dancers in plumes and leopard skins as well as by Zaire's president, Mobutu Sese Seko.

Mobutu, a baptized Catholic, was at odds with the church during his campaign in the 1970s to rid Zaire of colonial influence. In recent years, however, he has led a drive for reconciliation between church and state. With a Catholic population of 11.7 million -- 45 percent of the total population -- Zaire has more Catholics than any other African nation.

In a separate address to bishops, the pope defended the role of missionaries, cautioning the Zairian church against hasty "Africanization" of teaching and ceremonies and alluded to reports that some priests and nuns in Africa have not been following the rule of celibacy.

"Priests and members of religious orders must have solid convictions about the positive and essential values of chastity and celibacy," the pope said.

"They should be very vigilant in their behavior to be faithful without ambiguity to the commitment which they have made," he said.

Alluding to Zairian church services which incorporate dancing, drumming and ancestor worship, the pope advised the church to move slowly in its Africanization project aimed at making Christianity more easily understandable for Africans.

"This effort, which has all my confidence, needs much theological clarity, spiritual discernment, wisdom and prudence, and also time," the pope said.