No, a fast-food chain is not buying the Liberty Bell. But it sure seemed that way yesterday to thousands of people, who flooded phone lines in a sometimes panicky, often angry response to a giant corporate prank.

Without the barest suggestion that its tongue was planted in cheek, Taco Bell Corp. announced in full-page ads in The Washington Post and four other newspapers yesterday that it had purchased the historic symbol of American freedom and was renaming it the "Taco Liberty Bell." The chain even gave a seemingly high-minded reason for the purchase. It was, the company said, "an effort to help the national debt."

The only hint that the ad wasn't all it was cracked up to be was the date it appeared -- April 1. As in April Fools' Day. As in hoax.

Taco Bell seemed quite pleased by what came next. Callers jammed its headquarters in Southern California with anxious queries, with the news media stampeding close behind. Having snared everyone's attention, the PepsiCo Inc. subsidiary announced that it was all a joke, and that it was actually donating $50,000 for the upkeep of the Liberty Bell and launching a new ad campaign.

A Taco Bell spokesperson, as well as a company press release, boasted that the stunt was the biggest hoax since Orson Welles sprung his production of "War of the Worlds" on an unsuspecting national radio audience in 1938.

But others weren't in such a congratulatory mood.

"We were shocked. We had no idea this was happening," said Elaine Sevy, a spokeswoman for the National Park Service, which oversees the Liberty Bell exhibit in Philadelphia's Independence National Historic Park. "We have just been getting hammered with phone calls from the public."

Many of the callers were "alarmed," she said, believing that the ads were real in light of the shutdown of national parks during the recent federal budget crises. Among those who called the Park Service for reassurance were staff aides to Sens. Bill Bradley (D-N.J.) and J. James Exon (D-Neb.), and Reps. John Bryant (D-Tex.) and Howard P. "Buck" McKeon (R-Calif.). Firing back, Park Service Director Roger Kennedy called the ad "as false as it is cheesy."

As for Taco Bell's $50,000 donation, the Park Service is thinking twice. "Nothing has been finalized on that," Sevy said.

The White House, meanwhile, took it all in fun. "We will be doing a series of these," presidential spokesman Michael McCurry told reporters. "Ford Motor Co. is joining today in an effort to refurbish the Lincoln Memorial. . . . It will be the Lincoln Mercury Memorial."

Hey, he's only kidding.

Callers to the Post generally said they were fooled at first by the ad. But then surprise seemed to give way to anger that the chain had appropriated a national symbol for a publicity stunt. "It's a cute April Fools' joke, but it's in bad taste," said Bob Redmond, an attorney in Tysons Corner. Said Lucille Knowles, a District resident, "What bothers me is that it's almost believable. . . . Commercialization seems to be overtaking everything."

The plausibility of Taco Bell's hoax might stem from several factors, observers said, including the ongoing federal budget stalemate and the continuing encroachment of advertising into all corners of life.

Corporate sponsors have long sought to align themselves with many kinds of civic projects, buildings and public events -- from sports arenas to art museum exhibits -- in pursuit of favorable public relations. And many national symbols have been "borrowed" to sell products. A new TV commercial shows the Statue of Liberty seemingly coming to life to examine an Aurora luxury car parked on a passing ferry; a recent print ad featured radio talk show host Rush Limbaugh as a figure on Mount Rushmore. Taco Bell's "kind of spoof is made in a culture where the truth or falsity of any ad is difficult or impossible to tell," said Ronald K. L. Collins, a law professor and coauthor of "The Death of Discourse," a forthcoming book about commercialization and free speech. "It's precisely that kind of mind-set that they are playing on."

Whether the public gets the joke or not, Collins said Taco Bell will have achieved its aims: "They now have gotten themselves name recognition or association with a national symbol. Where do we draw the line? If this is merely being playful, you have to wonder if next time, someone might do the same thing with a crucifix." CAPTION: A park guide explains the history behind the Liberty Bell in Philadelphia yesterday.