The plan involves raising the tower - which leans about 15ft out of true - by half a degree, or 16in. The project was approved a month ago by the official committee for the protection of the Tower of Pisa, chaired by Professor Michele Jamiolkowski. The committee has been examining schemes since 1990 and is keen to have a solution in place in time for the millennium.

Opponents are alarmed by the committee's decision to pull the tower back towards the vertical by encircling it with giant steel cables or braces. The cables, 338ft long and 4in thick, will be attached to the tower at a height of 72ft.

The tower, which began to tilt dangerously after the last attempt to reverse its decline three years ago, is kept in place by 900 tonnes of lead weights piled against its base on the opposite side from the way it leans. If the steel cables prove successful, the committee's experts say, the lead weights could be removed next year, and soil will be removed from beneath the northern side in a series of "controlled landslides" to right the tower's base.

For the protesters, such as Professor James Beck of Columbia University and Professor Piero Pierotti of Pisa University, this is "irresponsible madness". An Internet site on the project has been inundated with protests and counter-proposals, and the ensuing row led the Italian press to dub the monument The Tower of Discord.

"The air of Pisa is full of poisonous accusations," said La Repubblica. Professor Beck, who holds the chair of art history at Columbia University in New York and heads ArtWatch International, which monitors art restoration projects, says that since 1990 £15 million had been spent on "temporary measures" which had "only succeeded in causing further damage".

He says the committee in charge of the tower had acted in haste because its mandate expires at the end of this year. It had, in any case, acted throughout its term in conditions of secrecy. "They do not consult the scientific community at large," Professor Beck says. "They have an authoritarian approach reminiscent of the Fascist era of Benito Mussolini."

Professor Pierotti, who has taught art history at Pisa for 40 years, agrees there is "no freedom of information".

In his book How Not To Save The Tower of Pisa (Una Torre Da Non Salvare), Professor Pierotti has examined the many schemes proposed over the past 150 years. The wackier proposals include attaching a helium balloon to the top of the tower, lopping off the top storey altogether, and relandscaping the surrounding meadow so that it slopes in the same direction as the tower leans and so makes it appear upright, an optical illusion which would presumably give the millions of tourists who visit Pisa every year a crick in the neck.

The tower, which is the campanile or bell-tower of the adjoining cathedral, was begun in 1173 in the Field of Miracles (Campo dei Miracoli). The tower, the cathedral (begun in 1064) and the circular baptistry form a trio of medieval masterpieces.

But just beneath the turf of the meadow is saturated sandy soil and clay, and the tower first started to subside when only 30ft high. Undeterred, masons continued the work, and the tower was completed after a further 180 years, with the bell-tower placed on top in 1350. Galileo, who came from Pisa, used the overhang to drop metal balls to prove the theory of gravity.

The tower has been declining slowly to the south ever since. In a modern echo, it started to shift ominously in September 1995 when the ground around it was deliberately frozen and workers started to remove rock and earth from the base to build a concrete ring. Frantic efforts by engineers working through the night staved off collapse, and the lead weights were successfully installed on the northern side.

The tower has a hold on the world's imagination, Professor Pierotti says, because its proportions are mathematically perfect - its eight storeys are intended to recall the Tower of Babel - and it is a work of "soaring imagination and symbolic beauty". He says that it is also "unquestionably a phallic symbol", an image that is emphasised by its angle. "Perhaps the attempt to pull it erect is another aspect of the age of Viagra."

Giorgio Croci, professor of engineering at Rome University and a member of the Tower of Pisa committee, says: "I am confident our plan will work."

Piero Floriani, the Mayor of Pisa, says he has "no fears that the tower will fall ... the committee is staffed by international experts whose credibility hangs on this plan."

Una Torre Da Non Salvare by Piero Pierotti is published by Pacini Editore, Via Gherardesca, Ospedaletto, Pisa, at 38,000 lire.