It's Super Bowl time in America, and Houston, the host city, is busy having an anxiety attack.

Don't misunderstand. Everything looks ready. Reliant Stadium, Houston's sparkly new football arena, is a $400 million, state-of-the-art, retractable-roofed marvel. Grand new hotels are booked and set to throw their doors open wide. Sublime restaurants are polishing the silver. Fabulous parties are scheduled to last for days.

No, the deep psychological rumbling in the nation's fourth-largest city is unrelated to Super Bowl plans, Super Bowl parties or Super Bowl football. Rather, Houstonians are fretting that tens of thousands of visitors and fans will sweep into town for Sunday's game only to find the Bayou City . . . super-ugly.

"People who move to Houston fall in love with this place, but before you get here you have a lot of misconceptions -- is it prairie? Is it a swamp? What the hell is it?" said Don Henderson, a native Chicagoan who arrived in Houston a decade ago and is now vice president and managing director of the Hyatt Regency Houston, as well as a key figure in the city's Super Bowl Host Committee. "Maybe more than any other city I've been in, people here care what [visitors] think of them. . . . Sure, it's insecurity."

Already, snarky out-of-towners are making comments. "Featureless terrain, uncontrolled sprawl, billboard-cluttered freeways," sniffed the Dallas Morning News. That reminded Houstonians of the New York Post's screaming headline about the city a decade ago: "This Place Is a Hellhole!"

Even brutally frank locals have gotten into the act lately. "We have essentially nothing to offer in terms of physical landscape," said Dan Barnum, a local architect who provoked a flurry of angry letters to the editor when he wrote, in an essay for the Houston Chronicle, "We have no aesthetic roots, no aesthetic foundation, so we don't complain when there is ugly around us -- it's expected and accepted."

Now, after months of feverish preparations, including a beautification campaign on a scale to make Potemkin blush, the subtext of much of Houston's civic conversation these days is: Will they like us? And what if they don't?

Like an ungainly adolescent determined to shine at the prom, Houston is going to extravagant lengths to primp for the big event. More than 20,000 trees have been planted along the freeways since October, the idea being to filter the billboard-and-motel-clogged frontage roads from visitors driving in from the airports. Taxi and limousine drivers have been coached to avoid the most unsightly stretches of road, and new highway ramps have been rushed to completion. Hundreds of volunteers have swept up some 25 tons of trash. Nearly 20 miles of streets and sidewalks downtown have had cosmetic overhauls, and Main Street's shabbiest old buildings have undergone facelifts including new facades and canopies. At Minute Maid Park, the city's new baseball stadium, workers have scrubbed the mold off the retractable plastic roof.

Even the citizenry itself has been instructed to spruce up. The new mayor, Bill White, last week decreed a smile campaign to convince the 100,000 expected guests that Houston is "the friendliest big city in the United States."

The smile campaign dovetails with what Super Bowl planners call a gleaming opportunity to "rebrand" Houston. "This city needs a shot in the arm, and this event is providing it," Chuck Watson, a former corporate executive who chairs Houston's Super Bowl Host Committee, told the Houston Chronicle.

The mayor's campaign and its syrupy slogan -- "Put Your Smile On. Company's Coming!" -- seem better suited to Singapore than the Lone Star State. After all, Texas is all about swagger. And many other U.S. cities, whatever their charms, tend not to subject themselves to bouts of self-doubt in the face of onslaughts of visitors. New Orleans, which has hosted nine Super Bowls, is a kind of slack-jawed party host, just waiting to pour the drinks and get the good times rolling. In New York, site of the Republican National Convention this summer, the prevailing attitude seems to be: How badly will these yokels mess up traffic?

Houston's unease seems all the more peculiar in what is, after all, one of the nation's most vibrant cities. In addition to its storied entrepreneurial verve (or excess: see Enron), Houston is endowed with terrific museums, world-class medical facilities, more theater seats for the performing arts than any U.S. city but New York, and a sleek new light-rail line -- to say nothing of sports venues that are among the most impressive in the country.

All that is a source of pride for Houstonians. But not enough, it seems, to mitigate the deep-rooted insecurity of a city that has often served as a punching bag for out-of-state politicians, headline writers and scholars of urban planning.

It is widely remembered here that Al Gore, in his presidential campaign four years ago, regularly bashed George W. Bush, then governor of Texas, by denigrating Houston as America's smoggiest city. And many Houstonians are convinced that despite professional packaging, solid financing and superb sports venues, Houston's bid for the 2012 Summer Olympics was undone because the city is unattractive. (Of course, the competition was stiff: New York edged out Houston as America's candidate to host the Olympics.)

"The experience . . . is that there are companies that ought to move here, and the CEO says it's a perfect place, but the key workers don't want to move here," said Stephen Klineberg, a sociology professor at Houston's Rice University who conducts an annual survey in the city on behalf of local corporations.

In fact, Houston is bigger, but not especially uglier, than many other cities in Texas, where developers tend to be unfettered by niceties such as zoning laws and a tradition of urban planning. In Houston's case, the city's contempt for zoning, and the absence of natural boundaries such as rivers or mountains, have contributed to a crazy-quilt blob of a place that sprawls anarchically for dozens of miles in every direction. Little attention has been paid until recently to public spaces, and vast wastelands of underdeveloped tracts in and around the city center connect oases of pleasant, sometimes graceful neighborhoods. Houston's 5 million people are spread out in a city a third as dense as Los Angeles.

The absence of zoning "preserved urban conditions that prevailed in U.S. cities in the 19th century, before the birth of land-use planning in the 20th century," said Stephen Fox, an architectural historian who teaches at Rice. "It promotes small-scale development and small-time real estate developers [and] islands of order in a chaotic, unzoned sea."

The foremost eyesore, Houstonians admit, are the highway frontage roads leading in and out of the city, garish bands of shopping strips, parking lots, car dealerships, fast-food joints, tattoo parlors and motels, all overhung with riotous billboards. Those freeways provide most visitors with their first glimpse of Houston, much to the chagrin of the city's Super Bowl planners.

This is not the first time that Houston has undergone a fitful spruce-up and anxious self-examination of its aesthetic shortcomings. The city suffered similar spasms before it hosted the Group of Seven conference of industrialized nations in 1990 and the Republican National Convention in 1992.

But the Super Bowl is the mother of American sports events, attracting 4,000 journalists and a worldwide television audience estimated in the hundreds of millions. It is Houston's first Super Bowl since 1974, when the game was played at Rice Stadium. This time, there is a sense that the Super Bowl has presented Houston with a tremendous opportunity freighted with the risk of humiliation.

"We must stage the best Super Bowl ever, perhaps by a factor of two, to win the right to land another any time soon or to sell skeptical guests on a return visit without a sports hook," wrote Dale Robertson, a Houston Chronicle sports columnist. "Houston's ugly side will be in everyone's face. . . . We might welcome a pea-soup fog."

Determined to put its best foot forward, planners arranged for days of parties and events leading up to the big game. At downtown's George R. Brown Convention Center, fans are indulging their NFL fantasies by meeting pro stars and playing video games at an interactive theme park called the N.F.L. Experience. On Saturday, the "Taste of the N.F.L." food festival will feature dishes prepared by chefs from every one of the league's 31 cities at Reliant Arena, just next to the football stadium. Even the renowned Museum of Fine Arts is getting into the act with a photo exhibit documenting the inaugural season of the local expansion team, the Texans. "First Down Houston: The Birth of an N.F.L. Franchise" consists of black-and-white photos of practices, players, teem meetings and fans.

The pregame highlight is the Main Event, a four-day party starting Thursday that is expected to fill the streets nightly with free concerts by 36 music groups performing on two outdoor stages. A 16-block area downtown will be closed to traffic.

With final preparations underway, many Houstonians agreed that the city has never looked better, even as they worried what visitors would think. And no one even blinked as ads for the mayor's smile campaign blanketed the town. On billboards.

Houston's Main Street, shown in November 2002, was torn up to make way for a light-rail line. Planners say Sunday's Super Bowl gives the city an opportunity to "rebrand" itself.Houston has been cleaning up its image to host Super Bowl XXXVIII at Reliant Stadium. Nearly 20 miles of streets and sidewalks have been overhauled.