SHANGHAI, China — The mammoth World Expo 2010, which just opened here, offers a terrific opportunity for U.S. public diplomacy — reaching out to millions of Chinese via our exhibition.

Yet the United States, alone among the world's leading countries, nearly had no pavilion at the Expo, because of congressional restrictions that make it almost impossible to use federal funds for world's fairs.

We were the last country, out of 200, to confirm attendance, provoking criticism in the Chinese media. Beijing would have taken our absence as a deliberate insult.

The U.S. pavilion finally got built after a determined push by Secretary of State Hillary Clinton, who was here Saturday as part of a trip aimed at deepening U.S.-China relations. "Establishing an American presence at this Expo worthy of our great country was quite a journey," she told an audience of U.S. corporate sponsors who had ponied up $61 million in a last-minute private fund-raising drive to build the pavilion.

Having spent a day talking to Chinese visitors at the U.S. exhibit, I think the journey was worthwhile.

Why so? Because, while the 2008 Beijing Olympics sought to introduce the world to the new China, this Expo will introduce the Chinese people to the world. Beijing officials have set a goal of 70 million mostly Chinese visitors (they want to well surpass the attendance at all past expos) and are busing in workers and farmers from far-flung provinces. This presents a unique chance to expose a broad swath of Chinese to U.S. ideas.

Congressional restrictions on funding for world's fairs may make sense (especially during a recession) if they are held in countries where we have long-standing ties, says Franklin Lavin, the volunteer chairman of the steering committee for the USA Pavilion at the Shanghai Expo. But not in a country such as China.

"Here, there is an enormous hunger to understand the United States ... to define the relationship," said Lavin, who is fluent in Chinese and has served in senior government posts dealing with Beijing. "So you need to reach out."

The Chinese eagerness to see the U.S. exhibit is evident in the long lines that zigzag in front of the building, with a wait of at least 90 minutes. The shiny silver facade of the pavilion, with a waterfall cascading down its front, may not be as dramatic as many of the other countries' buildings, but Chinese visitors eagerly pose for photos under the huge, red "USA" on the front.

As for the presentations inside — three large rooms with multiscreen film offerings and a fourth with interactive video displays by corporate sponsors — they represent a creative gamble. There is no sensational physical exhibit of American technology, but rather a subtle presentation of ideas.

One film shows Americans from all walks of life and ethnic backgrounds, starting with basketball superstar Kobe Bryant, trying to say "Hello" in Chinese — and laughing at their mistakes. The film is introduced by Hillary Clinton and includes warm remarks about U.S.-Chinese partnership by President Obama, at which point Chinese viewers' cameras start snapping.

A second multiscreen movie tells a story about the struggle of a young girl in a U.S. city who decides to make a trash lot next to her apartment building into a community garden. Slowly, she wins over her reluctant neighbors, again from a variety of ethnic communities and walks of life, who become a cooperative team.

"We knew people would like whiz-bang," said Lavin, "but we felt if we had one thing to say, it's about the magic of how our society works — the civic behavior."

I must admit I wasn't certain that Chinese visitors would get the message that citizens can work together for change without being directed by their government. Yet, in conversations with a couple dozen Chinese visitors, I heard comments such as "Even a little girl can make a change" and remarks about "the American spirit of cooperation" and "working together to make things better." Many approved of the film's "message to protect the environment."

And Chinese visitors were eager to pose with members of a group of 70 Mandarin-speaking American students who take turns introducing the films.

"America has a special hold on the Chinese imagination, and even where they don't agree, they want to understand," Lavin told me. After talking to the Chinese visitors, I'm convinced he is correct, which is why it's so fortunate the U.S. pavilion opened after all.

Trudy Rubin is a columnist and editorial board member for the Philadelphia Inquirer.