When modern structures meet ancient cultures

The neon letters, large as any Las Vegas sign, rise above a massive awning: ''International Preferred . . . Laundry.'' Behind the fancy facade stands a lone Arab laundress bent to her tub against the empty desert of Arabia.

The cartoon's message is clear to the student of third-world design: When East meets West, the architecture is irrelevant if not ludicrous.

Indeed, it is the major building dilemma of the last quarter of the 20th century.

The architectural quarterly Mimar, which showed the cartoon, put it this way: When ''the fast-talking from the North'' speaks of solutions, ''the wrapping is attractive, the catalogs hypnotizing, and the material benefits overwhelming.'' But the impact on the cultural heritage, ecology, and ambiance is a disaster.

How to stem this assault, how to team modern structures to ancient cultures and aesthetics would seem as tough as shaping the sands that surround the cartoon's fake facade.

Yet these are precisely the issues the Aga Khan - the leader of 12 million to 15 million Ismaili Muslims - is addressing. In less than a decade, the Muslim leader has made a valiant effort to solve these problems with humanity and intelligence.

In acknowledgement of his program of prizes, seminars, university programs, and the magazine Mimar aforementioned, the Aga Khan received two of the most prestigious prizes in American architecture recently. He was given the Thomas Jefferson Award, awarded for the first time to a patron of architecture in ceremonies at Monticello; and the American Institute of Arts honor award, acknowledging his efforts to ensure the fit of ''contemporary architectural technologies with Islamic tradition.'' The Aga Khan's programs - the Harvard-MIT Aga Khan Program for Islamic Architecture and the $500,000 Aga Khan prize given for specific buildings - have tried to improve the lot of 25 countries, ''to better the quality of Muslim life.''

But it is a stiff challenge. The quality of Muslim life is even now eroding: ''Between 1950 and 1974, the world's population grew from 2,500 million to 4,000 million,'' the Aga Khan told the Virginia audience for his Jefferson award. ''By the turn of the century, it will be 6,000 million, and of those people 80 percent will be in the third world, the vast majority of them rural dwellers. They represent a housing problem of immense dimension.''

And, yet, pausing for an interview in the midst of his prize-collecting trip to America, the gracious Harvard-educated leader deals with such issues in a calm, quietly-modulated way that belies their difficulty. He retains a belief in the power of education to address, if not solve the massive problems of his people. And since 1977, he has continually expanded ways to nurture an architecture aware of Islamic culture yet comfortable with the 20th century.

The Aga Khan Awards program last spring, for example, announced its second selection of ''culturally appropriate'' buildings. They appear dazzlingly attractive.

Sherefudin's White Mosque, for one, described as a prominent architectural landmark of the Muslim Bosnian town, is lauded as a religious and educational center. Yet it also stands like striking sculpture amid the small town. Similarly, another religious building, the Great Mosque in Niono, Mali, looks like splendidly contoured sand castles. Both buildings display handsome forms by architects and builders unknown and unacknowledged in the Western world.

Still another winner, an improvisation on Western technology, serves pilgrims on an age-old religious journey: The tentlike shapes of the Hajj Terminal in Jiddah, Saudi Arabia - by Skidmore, Owings, & Merrill of Chicago - is a more 20 th-century solution, a transfer from West to East.

At once pragmatic and philosophical, the Aga Khan recognizes that attention should be given to this sort of high-visibility architecture. But he also stresses its less glamorous aspects: ''Insofar as people are poor, architecture should nevertheless dignify their strivings. Insofar as the role of woman is changing, architecture should intensify that experience.'' His prizes thus go to both the architect/builders and the communities who sponsored their new buildings.

Beyond prizes, the Aga Khan Program communicates and disseminates new information in conferences like last year's ''Continuity and Change, design strategies for large-scale urban renewal,'' and in studies at Harvard and MIT.

Criticisms do come. Architectural Record recorded the 1983 awards program's failure to give a housing prize. In years past, the absence of women has caused comment (today, three women head the Harvard-MIT program). Above all, one wonders whether any architectural program alone can solve the problems of shelter and culture in the tumultuous third world.

On this question, the Aga Khan concedes that the power of the architectural solution lacks proof positive. ''All you do is see that a family that moves from bad housing to acceptable housing makes progress.''