Somewhere in the Astrodome's quiet vastness lurk the echoes of its triumphal heyday -- of Muhammad Ali fights and Elvis Presley concerts, of Hubert Humphrey's 1968 presidential campaign rally and George H.W. Bush's 1992 nominating convention, of Evel Knievel's motorcycle jumps and Billie Jean King's defeat of Bobby Riggs in the 1973 "Battle of the Sexes."

But these days the Astrodome's silence is broken only sporadically, and the events there are a poor match for the arena once proclaimed the Eighth Wonder of the World. The other day, a local law firm held its annual softball game there. Not long ago, a baseball-themed bar mitzvah took place on the infield.

A marvel of 1960s engineering, the Astrodome was the world's first domed, climate-controlled stadium, and it immediately spawned dozens of imitators in cities across the country. Its fall from grace began in the '90s, when it lost its professional football and baseball tenants, the Oilers and Astros, to newer, sleeker stadiums elsewhere.

Since then, the Astrodome has stood in magnificent isolation, like a dowager clinging to her former hauteur as her old friends die or move away. This year, said stadium officials, the Astrodome will be lucky if it has even 15 or 20 days' worth of events.

"We've got some capacity," said a deadpan Willie Loston, executive director of the Harris County Sports & Convention Corp., the public agency that oversees the stadium.

The vastness of the Astrodome still impresses, but little else does. The plumbing is unreliable; the AstroTurf carpet is stained and coming apart at the seams; the seats are rusting on their moorings. The air conditioning still works, but only because it doesn't need to most of the time.

Saddled with such a dinosaur, the Astrodome's overseers are trying to engineer its rebirth. Last week, the Sports & Convention Corp. invited proposals for redeveloping the Astrodome -- and, in the process, for reinvigorating the most visible symbol of the United States' fourth-largest city.

But what to do with it? Houston hardly needs another big stadium. It already has two others, both of them state-of-the-art venues with retractable roofs, including Reliant Stadium, which is next to the Astrodome and home of the Houston Texans, an NFL expansion team. Nor does it need a new convention center; a massive one of those, known as Reliant Center, has been built at the same complex, Reliant Park.

"Any redevelopment plan of the Astrodome is going to be totally different than what it was used for in the past," said Mike Surface, a developer who is chairman of the board of the county's Sports & Convention Corp. "We're trying to hang on to some of the historical significance, but I don't know if people would recognize it as you and I know it today."

Surface and other officials have been careful to say they do not favor razing the Astrodome. Instead, they have suggested converting its grimy concrete filigree walls into a gleaming skin of glass and steel, and incorporating a hotel, restaurants and an arena that could accommodate ice events, horse shows, concerts and assemblies under the famous dome.

Others have suggested the Astrodome be transformed into a splashy museum of science and technology, a colossal shopping mall or a biosphere featuring a rain forest and botanical gardens.

"The only way a building gets a chance to become old and historical is not to tear it down," Loston said.

Still, doubts about the Astrodome's future have engendered a case of civic nerves here. That spiked last summer, when the U.S. Olympic Committee spurned Houston's (as well as Washington's) bid to host the 2012 Games. At the time, some said that without the Olympics, the Astrodome had no future.

The suggestion that the Astrodome may become something unrecognizable -- or, worse, that it may be torn down completely -- upset some Houstonians. The Astrodome may be just 38 years old, but to many people here, it is an unsurpassed icon of municipal history and a singular point of civic pride.

"I am a fourth-generation Houstonian and am tired of not seeing anything of history left in our city because of progress," wrote Susan Sattler, one of scores of people who put their names to an online petition called "Save the 8th Wonder of the World." "Where is our pride in our past?"

Another signatory to the petition took a harsher tone. "The Astrodome is the 8th Wonder of the World and you want to tear it down for parking?" wrote Frank A. Harbuck Jr. "What stupid idiots. Most of you probably aren't even from Houston."

The sensitivities can be traced to the Astrodome's opening in 1965, an event stamped in the memory of virtually everyone here old enough to have witnessed it. President Lyndon B. Johnson, a couple of dozen astronauts and assorted lesser celebrities attended the opening, an exhibition match between the Astros and the New York Yankees. The oohs and aahs of wonderment at the Astrodome's sheer mass inspired commentary in newspapers and magazines from coast to coast.

Ceaselessly compared to the Colosseum in Rome, the Astrodome was simply the most thrilling thing ever to happen to Houston, as its colorful creator -- a cigar-chomping Texas salesman, judge and politician named Roy Mark Hofheinz -- never tired of pointing out.

"No one can ever see this and . . . still think this town is bush league, that this town is Indian territory," he said.

Feverish locals marveled at its vast bulk (big enough to accommodate an 18-story building under the dome), its impressive ice plant (it could produce 36,000 pounds of ice a day), and its spectacular cooling system (which maintained an inside temperature of 72 degrees, with 50 percent humidity).

Of course, there were skeptics, including the young writer Larry McMurtry, an out-of-towner from the Texas Panhandle who likened the huge dome, then painted white, to "the working end of a gigantic roll-on deodorant."

The cavils were ignored, even if the place was imperfect. Outfielders found they couldn't follow fly balls under the skylight, so the ceiling panels were painted gray. That blocked the sunlight, killing the grass, so for two years, groundskeepers painted the dead turf green. Finally, Hofheinz had the grass replaced with a magic carpet he called AstroTurf.

Players hated it, and some said it caused injuries, but it all seemed to represent technological progress and a Texas-style future.

Eventually, critics would disparage the Astrodome as a monument to bad taste and synthetic sport. But Hofheinz, swaggering showman that he was, insisted the Astrodome would become America's Eiffel Tower. Hundreds of thousands of people paid to tour it. The Astrodome was replicated, and improved upon, in cities all over North America. In San Antonio and St. Petersburg, in Montreal and Seattle, domed stadiums rose inexorably.

Time, though, was unkind to the Astrodome. Newer, more advanced stadiums offered better sight lines, broader concourses and more intimacy than the cavernous Astrodome could manage. Unlike the Astrodome, which could handle baseball and football, newer stadiums were purpose-built for one or the other and offered better amenities for each.

The NFL Oilers decamped for Tennessee in 1996, changing their name to the Titans. The Astros, the expansion team that Hofheinz had lured to Houston with the Astrodome, moved in 1999 to a new downtown park known then as Enron Field, and now as Minute Maid Park.

The crowning blow came last year, when the $450 million Reliant Stadium opened just 200 yards from the Astrodome.

With its 8,000 club seats, ultra-luxurious suites, plasma-screen television monitors and digitally wired, up-to-date everything, Reliant Stadium practically shouted 21st century. Next to it, the Astrodome seemed a relic from the '70s, an eight-track tape in a compact-disc world. Reliant Stadium also boasts a retractable roof -- a first for an American football stadium. This year, the Astrodome's last major tenant, the Houston Livestock Show and Rodeo, moved to Reliant Stadium.

So now the Astrodome stands nearly unused, at a cost of $1.5 million a year in upkeep. Its seats are still painted red, orange and yellow, the colors of the "rainbow uniform" the Astros once wore -- but dropped in 1986. The AstroTurf carpet is so frayed that groundskeepers must sew it together with green thread. The last time a capacity crowd was there, for the annual rodeo show more than a year ago, the plumbing backed up on one side of the building and nearly overflowed.

"The Astrodome brought a major landmark to our community that we all shared pride and appreciation in," Surface said. "It has a special place in our history, but my job today as chairman of the corporation is to evaluate all the options and help make something new."

The Houston Astrodome is seen through a fish-eye lens in a photo taken in April 1965, the year the Astros played their first game there.The Astrodome's overseers have called for proposals to redevelop the 38-year-old structure, a source of historical pride for many in Houston.