They do things on a scale in the new Saudi Arabia - so grand, sometimes, that it would weaken the knees of public officials in countries less endowed with cash.

The latest example is the campaign to clean up the streets and alleys of Riyadh, a project that began under American supervision this month. When the city fathers of the royal capital decided they wanted to get rid of the trash and garbage blighting the landscape, they were willing to pay the price - a quarter of a billion dollars over five years.

That was the cost of hiring an Illinois company. Wast Management Inc., to plan and form a complete city sanitation department, recruit more than 2,000 workers in India to do the work, build a self-contained camp in the desert to house them, import 200 bright yellow American trash compacter trucks and distribute 120,000 plastic garbage cans.

"No place else in the world would do anything like this," said David Blomberg, resident manager of the joint venture that Waste Management formed with Pritchard of England, "and there is no place else where it would be necessary."

In effect, Blomberg is the sanitation commissioner of Riyadh, a fast growing, chaotic city of about 700,000 residents where the oil-fueled development boom has far outstripped the primitive public services.

Factories and houses are outrunning the utility lines as they spread into the desert and there never really was any organized trash collection system. Trash was piling up in the gutters, goats wandered among heaps of uncollected garbage and smoky fires burned over makeshift refuse dumps scattered around the city.

According to Blomberg, who once tried to interest Montgomery County, Maryland, in a scheme to haul its refuse out by rail. Waste Management Inc. faced problems here that a similar-sized American city would never have to deal with in confronting the trash problem.

Nobody knew, for example, just how mush trash and garbage Riyadh was generating or where. City maps were so outdated, he said, that "we had to send a team out to walk every street just to see what we were getting involved in."

For another thing, nobody in laborshort, Saudi Arabia was available to do the kind of work that was needed - sweeping the streets, emptying trash cans, operating compacter trucks, maintaining a sanitary landfull. In short, there are no Saudi garbage men. So the workers had to be recruited from a country where an offer of $250 a month plus free room and board would seem attractive - India.

"We sent 32 people to Bombay to recruit and test the workers," Blomberg said. "We were tough. If a man said he was a driver, we made him show us. We got thousands of responses to our ads."

He said the government of India cooperated in the recruiting and made a condition of their employment that 75 per cent of their wages be remitted directly to India, in hard currency. That represents no hardship for the workers. Blomberg said, because in their desert camp outside Riyadh, "there's nothing for them to spend money on except maybe cigarettes.

Since Saudi Arabia has an acute housing shortage, contractors who employ foreign workers must first build dwellings for them before beginnings the main projects. Saudi Arabia is probably the world's leading consumer of preabricated dwellings. Those in the Waste Management - Pritchard camp were made in Norway.

Except for water and food, which are trucked in, the garbagemen's desert camp is self-sufficient, sheltering the workers who live there and the fleet of new vehicles that will be stored and maintained there. It even has two swimming pools, one for the Indian workers and another for the British and American supervirsors.

City official's apparently realize that it is one thing to put out trash can and provide extra heavy lids that will not blow off in the sand stroms, and another to change the townpeople's habits.

Residents cheered when all 200 yellow trash trucks rolled through the streets in a parade, sporpting stickers on the doors saying "Help Make Riyadh Clean."

But when distribution of the trash cans began, the newspaper Al Riyadh sniffed, "regrettabley, some children, and perhaps some of their elders too, took possession of these bins and hid them in their houses . . . It is not quite understandable how the citizens expect to maintain the cleaniness of their capitcal city given such behavior, which only reveals the extent of ignorance and indifference to the municipality's effort to keep the city tidy."

But Blomberg is hopeful.

Strolling along the dusty sidewalks, he lifts the tops of the trash cans and is happy when he sees the candy wrappers inside instead of on the pavement.