Prince Karim Aga Khan, one of the world's richest men, is on a spending spree in some of the world's poorest countries because he thinks talk is cheap.

The Aga Khan is celebrating his 25th year as leader of the 15 million Ismaili Moslems scattered mostly across Asia, Africa and the Middle East by spending $60 million this year on Third World development projects.

While visiting Pakistan to open a $250 million university and medical center that he built in Karachi, the Aga Khan said he has little patience for the kind of North-South dialogue that was pursued elusively at the summit in Cancun, Mexico.

"As long as you talk about concepts rather than programs, you're just swimming in the ocean," he said in an interview here. "I prefer taking on specific issues and programs, one at a time, rather than engaging in an enormous dialogue. I'm somewhat skeptical about that."

As the 49th imam, or hereditary spiritual leader of the breakaway Ismaili sect of Shiite Islam, the Aga Khan is more visibly involved in improving the material welfare of his followers and their non-Ismaili neighbors than in tending to their spiritual needs.

During a week-long tour of Pakistan, he launched medical clinics and economic development projects in Karachi, Hyderabad and Faisalabad, bringing to 120 the number of health services facilities in Pakistan operated by the Geneva-based Aga Khan Foundation.

The foundation also sponsors some 400 clinics and education centers in India, Bangladesh, Tanzania and Kenya and has development projects in several Third World countries.

But for all his philanthropy and a jump in charitable spending from $20 million last year to three times that this year, the Aga Khan admits to having an image problem.

He is probably better known in the West, he concedes, for his thoroughbred race horses, including the kidnaped $20 million stud Shergar, or by association with his father, Prince Ali Khan, whose jet-setting life style and marriage to Rita Hayworth made newspaper headlines before he was killed in an automobile accident in Paris in 1960.

The prince is also commonly associated with his grandfather, Sultan Mohammed Shah Aga Khan, who in his 72 years as the Ismaili imam used to celebrate his key anniversaries spectacularly by being weighed in gold, diamonds and platinum.

His image in the West, the Aga Khan said, reflects in part a lack of knowledge in much of the developed world of the problems and hopes of the developing world.

"The West has to be willing to learn. Until a wider base of the intelligentsia becomes knowledgeable about the Third World, there will be no response," he said.

The Shiite Ismailis hold that Ismail, the seventh in descent from the Prophet Mohammed's cousin and son-in-law, Hazrat Ali, was the last of the revealed imams and that the Aga Khan is the hereditary successor of the unrevealed imams.

For several generations they have had a tradition of not only representing a progressive minority of the Shia branch of Islam, but also of making themselves essential to the communities of the 25 countries that comprise their diaspora.

Some Islamic scholars ascribe the Ismailis' relentless philanthropy to an attempt to get along with the Sunni Moslem-dominated communities in which they live and thus fend off religious persecution.

The Aga Khan, who was born in Geneva and studied Islamic history at Harvard, dismissed that notion in the interview, saying that divisions in Islam have existed for centuries and that neither he nor his grandfather had ever regarded their minority sect menaced by religious differences with the rest of the Islamic world.

He said he had no objection to state-directed Islamization campaigns that do not attempt to legislate the practice of faith in an arcane manner.

"I have no problem with the concept of encouraging the practice of Islam within a modern context in all areas; I have no argument at all," the Aga Khan said, adding that some of the Moslem countries undergoing Islamization had been subjected to centuries of colonial, non-Islamic domination and have a right to return to Islamic values.

The problem arises, he said, in determining a "practical definition and implementation" of Islamic law that is acceptable to all Moslem sects in the country and is not repugnant to Islam.

"To develop that law requires a lot of time, reflection and wisdom," he said.

The Aga Khan also said he saw no conflict between the progressivism of his sect and the military dictatorship of Pakistani President Mohammed Zia ul-Haq, with whom he has closely allied himself.

"The western world has lived through periods of weak and disorganized democracies, and the countries that have suffered from undisciplined democracy have paid and are paying a very expensive price," he said.

Countries of the developing world, he added, have had the same experience and have "turned to organized bodies" for a remedy, the organized bodies being their armies.

"I believe in democracy, but where an undisciplined democracy has failed to produce a satisfactory result, it looks for a solution where it can find one," he said.