One Laptop Per Child, an ambitious project to bring computing to the developing world’s children, has considerable momentum. Years of work by engineers and scientists have paid off in a pioneering low-cost machine that is light, rugged and surprisingly versatile. The early reviews have been glowing, and mass production is set to start next month.

Orders, however, are slow. “I have to some degree underestimated the difference between shaking the hand of a head of state and having a check written,” said Nicholas Negroponte, chairman of the nonprofit project. “And yes, it has been a disappointment.”

But Mr. Negroponte, the founding director of the M.I.T. Media Laboratory, views the problem as a temporary one in the long-term pursuit of using technology as a new channel of learning and self-expression for children worldwide.

And he is reaching out to the public to try to give the laptop campaign a boost. The marketing program, to be announced today, is called “Give 1 Get 1,” in which Americans and Canadians can buy two laptops for $399.

One of the machines will be given to a child in a developing nation, and the other one will be shipped to the purchaser by Christmas. The donated computer is a tax-deductible charitable contribution. The program will run for two weeks, with orders accepted from Nov. 12 to Nov. 26.

Just what Americans will do with the slender green-and-white laptops is uncertain. Some people may donate them to local schools or youth organizations, said Walter Bender, president of the laptop project, while others will keep them for their own family or their own use.

The machines have high-resolution screens, cameras and peer-to-peer technology so the laptops can communicate wirelessly with one another. The machine runs on free, open source software. “Everything in the machine is open to the hacker, so people can poke at it, change it and make it their own,” said Mr. Bender, a computer researcher. “Part of what we’re doing here is broadening the community of users, broadening the base of ideas and contributions, and that will be tremendously valuable.”

The machine, called the XO Laptop, was not engineered with affluent children in mind. It was intended to be inexpensive, with costs eventually approaching $100 a machine, and sturdy enough to withstand harsh conditions in rural villages. It is also extremely energy efficient, with power consumption that is 10 percent or less of a conventional laptop computer.

Staff members of the laptop project were concerned that American children might try the pared-down machines and find them lacking compared to their Apple, Hewlett-Packard or Dell laptops. Then, in this era of immediate global communications, they might post their criticisms on Web sites and blogs read around the world, damaging the reputation of the XO Laptop, the project staff worried.

So the laptop project sponsored focus-group research with American children, ages 7 to 11, at the end of August. The results were reassuringly positive. The focus-group subjects liked the fact that the machine was intended specifically for children, and appreciated features like the machine-to-machine wireless communication. “Completely beastly” was the verdict of one boy. Another environmentally conscious youngster noted that the laptop “prevents global warming.”

Still, the “Give 1 Get 1” initiative is mainly about the giving. “The real reason is to get this thing started,” Mr. Negroponte said.

He said that if, for example, donations reached $40 million, that would mean 100,000 laptops could be distributed free in the developing world. The idea, he said, would be to give perhaps 5,000 machines to 20 countries to try out and get started.

“It could trigger a lot of things,” Mr. Negroponte said.

Late last year, Mr. Negroponte said he had hoped for orders for three million laptops, but those pledges have fallen short. Orders of a million each from populous Nigeria and Brazil did not materialize.

Still, the project has had successes. Peru, for example, will buy and distribute 250,000 of the laptops over the next year — many of them allocated for remote rural areas. Mexico and Uruguay, Mr. Negroponte noted, have made firm commitments. In a sponsorship program, the government of Italy has agreed to purchase 50,000 laptops for distribution in Ethiopia.

Each country will have different ideas about how to use the machines. Alan Kay, a computer researcher and adviser to the laptop project, said he expects one popular use will be to load textbooks at 25 cents or so each on the laptops, which has a high-resolution screen for easy reading.

“It’s probably going to be mundane in the early stages,” said Mr. Kay, who heads a nonprofit education group, whose learning software will be on the XO Laptop. “I’m an optimist that this will eventually work out,” Mr. Kay said.