In one of his more imperial decisions, the late Francois Mitterrand waved the wand of French presidential authority and announced, out of the blue, the construction of "perhaps the largest, most modern library in the world".

Not even prohibitive cost or a change of government has since stood in the way of this decision. Ten years on, the FFr8bn (£960m) Bibliotheque nationale de France (BnF) is virtually complete, sited by the Seine at the east end of Paris.

Last month, the research facilities and a 2,000-seat reading room - the core of the library - were inaugurated. Simultaneously, the BnF was linked to the centre of Paris by a new metro line with high-speed driverless trains, so ending the library's isolation on the edge of a grim industrial wasteland.

It has been an extraordinary example of the French administrative machine being girded into action for a great national purpose - from planning the site through to moving 11 million volumes and 1 million documents from the existing library at the old Richelieu building in central Paris into the new premises. The stop-go construction history of the new British Library in London scarcely bears comparison.

Not everything, however, is running as smoothly at the site. Unions have been staging strikes in protest at the lack of preparation for such a complex venture.

Library staff complain that the opening was dictated by a political timetable, without reference to proper testing of, and training on, all the highly sophisticated computerised technology. These embarrassing protests could compromise the library's ambitions to open six days a week from 9am to 8pm.

One of the many problematic novelties is a smart card given to readers once they have registered, which enables them to reserve seats and order books delivered in automated containers. The workload is proving too heavy, and the order time for books from the stock rooms, containing 395km of linear shelving, has been up to four hours instead of the promised half-hour.

"There are inevitable start-up problems which we will have to iron out," says Francois Stasse, a senior civil servant who became BnF's director-general in September. He believes the best way of testing the system is via live practice, but acknowledges that the architect has not made life easy for staff: "We will have to devote attention to improving the working conditions of the staff, too many of whom have to work shut off from daylight."

The architect, Dominique Perrault, is blamed for putting the comfort of the reader ahead of staff comfort. More generally, everyone is having to adjust to the building being a triumph of design over functionality.

The design is a neat visual conceit. Four glass towers, each in the shape of an open book, stand at the corners of a high podium covered by wooden planks like a ship's deck. Each tower serves in large part as book storage, and the architect wanted the public to see the books through the glass.

However, it was impossible to find adequate insulation against sun heat, and wooden shutters have had to be introduced. Furthermore, since book conservation limits room temperature to a maximum of 18C in the glass towers, it can be chilly for staff in winter.

The most successful aspect of the library is the deliberate contrast between the bleak exterior overlooking the industrial reaches of the Seine and the other-worldly tranquillity inside. Unseen from street level is the central area of the podium - a huge hollow rectangle with a sunken two-acre garden.

Here, the architect has sought to create the sense of a medieval cloister, with all reading facilities looking on to this inner garden through uninterrupted glass fronting. The air of monastic contemplation was one of the most insistent requests of Mitterrand, a keen bibliophile who used to slip off from official duties to browse in Paris bookshops.

The novelty of the Mitterrand library project is the opening of reference material to le grand public - anyone over 16. Thus, the upper level of the space round the "cloister" can seat 1,700, consulting, free of charge, a range of 5,000 periodicals and an eventual 370,000 reference books. This has been operating for almost two years.

The researchers are housed below le grand public at ground level with the cloister garden. Essentially, anyone who can demonstrate a need for access to specialised material or the collection of 200,000 rare books is given a card (the annual fee is a token FFr300). The 2,000 seats for researchers reflect both the fact that French university libraries have not been so strong as, say, in Britain or the US, and that Paris accounts for 26 per cent of the country's student population.

One of the main unresolved problems is how the library's FFr1bn annual operating funds (10 per cent of the culture ministry's annual budget) should be deployed between acquisitions and conservation. The demands on conservation are huge because of the quality of paper used in books from the mid-19th century to the 1960s.

This paper, manufactured from wood pulp, is brittle and heavily acidified. The BnF reckons that of the two million books published in France between 1875 and 1960, 90,000 have been lost. A further 580,000 are at risk in the short term and 600,000 in the medium term.

"Conservation is very costly and we will have to choose in many cases between full restoration of these books or preservation on micro-film or through digitalisation," says Stasse.

Another drain is the conservation of audio-visual material also housed at the library. By law, seven French TV channels have been obliged since 1995 to deposit programmes. These are being accumulated at the rate of 17,000 hours a year, plus a further 23,000 hours of radio. In trying to span the printed and audio-visual worlds, those behind the library have almost certainly underestimated the impact of the audiovisual boom.

But the library is meanwhile devoting huge resources to state-of-the-art cataloguing of items collected over the past five centuries. (France first established the principle of printers being obliged to deposit copies of books for the royal library in 1537.)

By next year it is hoped to have eight million electronic entries covering all printed and audio-visual material in the Mitterrand complex, as well as part of the collection that has been digitalised.

A link is also being provided with the specialised collections left in the old library building - antiquities, coins, maps, manuscripts, music, performing arts, photographs and prints. In tandem, a French Union Catalogue is being compiled, putting on a database the main documents held in French university and rich municipal libraries.

Part of the catalogue and material is already available on the internet through a special server (htp://gallica.bnf.fr/), and the BnF is co-ordinating with foreign libraries to share information.

Problems of copyright, plus the need to protect traditional publishers' business, however, are liable to limit for the time being the amount of texts available to the public via the net.

This encourages librarians at the BnF to stake their continued faith in the printed word. But architect Perrault has an even bigger stake. He has made himself a hostage to fortune by choosing an open book design to symbolise the library at precisely the time electronic publishing is gathering pace.