VENICE - Legend has it that the Bridge of Sighs, which connects the Palazzo Ducale here to an ancient prison, got its name because it gave convicts on the way to serve their sentences a last glimpse of the limpid lagoon. 

The view today, however, is more likely to be a gargantuan billboard on a blue sky of tarpaulin touting Bulgari or Coca-Cola.

Behind the cloud-studded blue are the facades of fragile monuments under restoration; those structures are also the beneficiaries of the advertising revenue.

But when the Coke billboards went up this summer on buildings that abut the Piazza San Marco - the historic and, perhaps more to the point, touristic, heart of Venice - there was an explosion from outraged Venetians.

"We couldn't stay quiet," said Maria Camilla Bianchini d'Alberigo, president of a heritage protection association. "Too much is too much." Her organization, the Fondo Ambiente Italiano, denounced the intrusiveness of the ads, setting off the public debate.

"What's missing is a set of criteria that makes the advertising compatible with the environment so that the buildings are not offended, and so that they are still visible," she said.

City officials counter that without these advertisements, the city could not begin to maintain its historic monuments, many of which show the ravages of centuries of wear, exacerbated by the impact of the watery setting.

Renata Codello, the Culture Ministry official responsible for Venice's monuments, said, "Ads pay for the restoration of public buildings," which would not get repaired otherwise, "even though many are a hazard for public safety."

"We're just not in a position to say no to money, not for aesthetic reasons," she said in a telephone interview. "I can't turn down the image of a bottle when there are pieces of the Palazzo Ducale falling to the ground."

Ms. Codello said her department had received $200,000 for restorations so far this year, well short of the $2.6 million to $3.9 million she requests annually to keep abreast of the most precarious situations.

But Venice, Ms. Codello added, has relatively few advertising spaces on scaffolding, compared with cities like Rome and Florence where billboards are far more prevalent.

The Culture Ministry has a budget of about $47 million for restoration of these sites, but Italy has a rich architectural heritage, and funds are always tight. Of that amount, $1.8 million was allocated to the entire Veneto region, which includes Venice.

Private sponsorship, once limited to financial contributions, became less restrictive under a 2004 law that allowed contributors to have direct involvement in restoration projects, including carrying them out. The change in the law has not had a huge effect as far as bringing money in, according to a Culture Ministry official, who spoke on condition of anonymity, in line with ministry policy.

While discussions persist in Italy on the extent to which business interests should intrude upon cultural undertakings, and though private enterprises have been active within the state-controlled system for more than a decade - through bookstores, restaurants and ticketing services - officials entrusted with preserving Italy's cultural heritage remain distrustful of commercial involvement.

When Mario Resca, who ran the Italian subsidiary of McDonald's for years, was appointed to a new ministry post to develop museums two years ago, there was a significant outcry that the ministry's mandate would be bartered for an entrepreneurial model.

And now the Italian government has been debating whether to turn over some properties, from mountains to army barracks, to local administrations, which have fewer restrictions on their patrimony.

"We can increase efficiency and improve results, but we can't commercialize everything," Alessandra Mottola Molfino, president of Italia Nostra, another heritage protection agency, said in a telephone interview. "The lesson that goes out is that there is a price for everything."