VATICAN CITY - A long-missing Michelangelo sketch for the dome of St. Peter's Basilica, possibly his last design before his death, has been discovered in the basilica's offices, the Vatican newspaper said yesterday.

The sketch, drawn in blood-red chalk for stonecutters who were working on the construction of the basilica, was done by the Renaissance master in the spring of 1563, less than a year before his death, L'Osservatore Romano reported.

"The sureness in his stroke, the expert hand used to making decisions in front of unfinished stone, leave little doubt, the sketch is Michelangelo's," the newspaper wrote about the discovery, which it said will be presented Monday at a news conference at the Vatican.

The sketch shows that Michelangelo "on the threshold of 90 years of age, even though he wasn't coming regularly to the [basilica] construction site, continued to take binding decisions" on how the work was being carried out, the Holy See's official newspaper commented.

The sketch "now becomes the last known design of the artist," the newspaper said.

Michelangelo, who began working on the basilica's construction in 1547, was in his late 80s when he did the sketch. The sketch is especially rare, the Vatican newspaper said, because the artist ordered many of his designs destroyed when he was an old man.

The sketch was discovered in the Fabbrica of St. Peter's, which contains the basilica's offices.

L'Osservatore Romano said most sketches by Michelangelo for the stonecutters were destroyed or lost in the cutters' workplaces.

Michelangelo apparently made the sketch for the stonecutters because he was dissatisfied with how some blocks of travertine were cut, the newspaper said. Travertine is a particularly resistant stone still used today in building homes and offices in Rome.

Michelangelo's design shows a spur of the drum of the dome to indicate to the cutters just how much stone needed to be hewn. Included on the sketch were three numbers - 6, 9 and 3/4 - but it was unclear what the figures referred to.

Michelangelo completed the dome and four columns for its base before he died in February 1564. Three weeks before he died, when he was nearly 89, he went up the dome to inspect it.

The construction of the basilica, whose cupola defines Rome's skyline, spanned several working lifetimes of some of the Renaissance's most celebrated artists and architects.

The first architect of the basilica, Donato Bramante, died eight years after the cornerstone was laid. Other architects, including Raphael, followed, until Pope Paul III turned to Michelangelo in 1546 - 32 years after the artist had put the last brush stroke on the Sistine Chapel's frescoed ceiling.