SHANGHAI — If it’s not the Greatest Show on Earth, then the World Expo opening next month in Shanghai is surely the biggest, in keeping with China’s striving to do everything on a gargantuan scale.

The fairgrounds sprawl over 1,300 acres, twice the size of the historic world fairs held in Chicago in 1893 and New York in 1964. Up to 450,000 visitors can be admitted a day, five times as many as at Disneyland in Anaheim. Not to be outdone by rival Beijing, Shanghai has spent $45 billion on an Olympic-size makeover.

Shanghai is trying to revive the grand tradition of world fairs, which in their heyday occasioned all sorts of wondrous inventions, such as the Ferris wheel (which debuted in 1893 in Chicago) and the Eiffel Tower, built as an archway for entrance to the Paris fair of 1889.

Since the mid-20th century, world fairs have lost much of their luster as air travel, television and the Internet became more efficient means of introducing people to new ideas.

But most Chinese don’t have the wherewithal to travel abroad, so for them, the World Expo might be their most personal encounter with other cultures. Chinese are expected to make up 95 percent of the 70 million visitors anticipated during the six-month run, from May 1 to Oct. 31.

“”The Olympics was China’s chance to showcase itself to the world. This is the world’s chance to show itself to the Chinese people,”” saidNick Winslow, the Pasadena, Calif.-based theme park expert who is president of the U.S. pavilion.

Participating countries are building lavish pavilions. Japan announced that it spent $133 million on a large, purple cocoonlike structure, a whopping sum considering that the pavilion will be demolished at the end of the expo. Saudi Arabia is rumored to be spending even more to re-create the Arabian Desert, complete with date palms.

Denmark is sending its famous “”Little Mermaid”” from Copenhagen’s harbor. It is the first time that the statue, inspired byHans Christian Andersen’sfairy tale, has been allowed to travel abroad.

“”China likes its coming-out parties. This is one more opportunity for the countries of the world to come and kowtow to a rising China,”” saidAdam Minter, a Shanghai blogger who has written extensively on the World Expo.

The pavilion designs are whimsical. The most highly anticipated, that of Britain, looks like an oversized dandelion puff: 60,000 acrylic rods swaying in the breeze.

The Israeli pavilion looks like a giant seashell; the Spanish, a wicker basket; the United Arab Emirates, a luminescent sand dune.

More than 180 countries are participating. To ensure that nobody failed to show up, the Chinese provided $100 million to subsidize exhibits by developing countries and built a pavilion for African countries to set up exhibits. (The United States was nearly a no-show because of bureaucratic bungling and congressional spending limits, but at the last minute pulled off a $63 million pavilion that will feature a Hollywood-produced “”4-D”” spectacle focusing on initiative.)

Out of deference to the host, none of the pavilions is larger than China’s, a 200-foot-high structure that looks like a traditional city gate in hues of imperial red. It towers above two small pavilions for the autonomous territories of Hong Kong and Macao, the former shaped like an ice cube, the latter like a crouching rabbit. Taiwan has a pavilion nearby.

In Shanghai, preparations for the expo have resembled a mass mobilization campaign, military-style. In less than a year, the city has doubled its subway tracks to 260 miles, built a new airport terminal and renovated the historic riverfront promenade, the Bund. The expo’s slogan is “”Better City, Better Life,”” and the event has been a catalyst for a collective housecleaning. The city has even gone door to door, repairing plumbing and covering unsightly air conditioners.

“”This is our culture. We know how to mobilize in a way that you (Americans) could never pull off,”” saidYu Hai, a sociologist at Shanghai’s Fudan University.

Not everybody in Shanghai loves the expo. Complaints about the inconvenience of the construction, the dust, the noise and the traffic have been voiced by many residents but, as is typical in China, quickly silenced. Protests by hundreds of people whose homes were demolished in preparation for the expo were rapidly suppressed.

“”The expo site contained very polluting factories that did not belong on very valuable riverfront land in the center of the city. Removing the ugly flyover bridge on the Bund gave it at least partly its old appearance back,”” saidJohannes Dell, a German architect in Shanghai. “”I think the city planned this very appropriately.””

Shanghai is also hoping to avoid the stifling security presence that threatened to squeeze the fun out of the 2008 Olympics. Concerned about possible terrorist attacks or even protests, China sharply limited visas and controlled neighborhoods near Olympic venues so thoroughly that many restaurants and shops had to close.

Although security will be tight for the expo, China so far has not limited visas.

“”Compared with the Olympics, the expo will have a richer culture,”” said Zhu Yonglei, deputy director-general of the Bureau of Shanghai World Expo Coordination. “”It will be more interesting.””