Pope John Paul II embarks on his third trip to Africa in five years Thursday hoping to reinforce the Roman Catholic Church against a growing Islamic revival on the continent the Vatican considers one of its success stories of this century.

In the face of this revival, the 65-year-old pontiff, who will be making a 12-day swing through seven nations, is expected to urge his African bishops, priests and followers to step up their already highly successful evangelization efforts.

While diplomacy, formal commitments to ecumenism and a desire to foster cooperative relations with Islam will restrain the pope from speaking out directly on the issue, senior Vatican officials quietly have made known that the competition between Roman Catholicism and Islam for converts in Africa is one of the church's major concerns.

The Islamic renaissance is being felt in a wide belt across central Africa from Sierra Leone on the Atlantic Ocean to Sudan on the Red Sea.

One of the pontiff's key themes, according to Vatican sources, will be the proclamation of the "second evangelization" of Africa during his whirlwind series of formal masses, conferences with national church hierarchies, meetings with local priests and exhortations to the faithful.

The pope also will consecrate a new cathedral in Ivory Coast, ordain priests in Togo, beatify a nun in Zaire and visit a game park in Kenya.

Making his 27th trip abroad since assuming the papacy in 1978, John Paul will visit Morocco, Togo, the Central African Republic, Cameroon, Ivory Coast, Zaire and Kenya -- the last three countries for the second time.

All are relatively stable and prosperous by African standards and have not been affected greatly by the crippling famine that has struck many of their neighbors.

Vatican sources said the pope had hoped to visit Sudan, one of the poorest nations worst hit by famine, but the country's Moslem rulers declined to invite him.

The importance the pope attaches to Africa stems from the fact that while Islam is the continent's largest religion, Roman Catholicism is growing faster there than on any other continent.

"Along with Latin America, Africa is considered one of the reservoirs of world Catholicism for the future," Vatican spokesman Joaquin Navarro Valls said in an interview this week.

"All you have to do is look at the figures," Navarro said. "In 1901 . . . there were only 1.1 million Catholics in all Africa, making up about 1 percent of the continent's population. Today we are adding about 2 million Catholics a year, and there are a total of 65 million Catholics on the continent, or 16 percent of the total population. By the end of the century, we expect to have 100 million," he said.

The reason for the church's success in Africa, Vatican officials point out, is the inherent spiritualism of Africans. "The average animist in Africa is much more spiritual than the average Catholic in Europe," said one Africa specialist at the Vatican.

"Africa is the only continent . . . where you can't find any atheists or agnostics," Navarro said, "People in Africa are by nature a religious people -- they are prepared for Christianity."

The church also sees Christianity as a force that can unite the diverse, often antagonistic tribes and linguistic groups that make up the nations of modern Africa.

"In Africa the tribal bonds are stronger than the national bonds," Navarro said. "You need something that can be a homogenizer to unite the country and we believe -- and many African political leaders also believe -- that Christianity -- or Islam -- can do that."

While the competition with Islam will not be discussed openly, a senior Vatican source described one way the pope will deal with the problem. In a country such as Togo, where Moslems predominate in the nation's north while Christians are the dominant religious group in the south, the pope will urge his bishops and priests to move into the north to proselytize among the non-Moslems.

"The messsage will be," the source said, "that no fertile ground for converts should be left untouched, even if it is in a Moslem-dominated area."

In Kenya, John Paul will close the 43rd International Eucharistic Congress, which is expected to draw up to 50,000 Catholic pilgrims from around the world.

Before returning to Rome, the pontiff will stop at Casablanca, Morocco, at the invitation of King Hassan II to address an audience of predominantly Moslem youths.