ROME (AP) _ The Italian semiannual high fashion shows opened in Rome Monday, with the big news that Gianfranco Ferre, one of the top names in ready-to-wear, is taking the giant step onto the couture runway.

Ferre's clothes have long been hailed by fashion critics as wearable works of art.

When the 41-year-old Milanese designer and former architect presents his fall-winter 1986-1987 collection Tuesday night, he will become the first big name designer to go from ready-to-wear to couture.

The reverse has been common practice for over a decade, with such prestigious high fashion names as Valentino in Italy, and Yves Saint Laurent in France making their ready-to-wear fortune off their couture label.

''Where style and price tag are concerned most of ready-to-wear evening clothes were already in the high fashion bracket,'' said Ferre in a recent interview. ''Throw away the sewing machine and bring in the old time seamstresses combined with the best in Italian fabrics, and you create couture,'' the designer added.

The 81 outfits he will present Tuesday night in the elegant gardens of the Palazzo Pallavicini, in downtown Rome, have been carefully stitched together by artisans brought by the designer to Milan from Turin and Bologna.

Aside from the Ferre premiere, the week promises to revive the best in high fashion elegance, with ancient palazzos as stages for the couture runways, elegant dinners in lavish Roman courtyards, and a finale of fashion fantasy with couture outfits from the past and present paraded down Rome's most famous staircase, the Spanish Steps.

Among the 12 top names in Italian high fashion showing this week is the veteran Valentino, undisputed king of Italian couture.

Seemingly unruffled by the challenge to his throne, Valentino graciously sent Ferre a handwritten invitation to attend the presentation of his collection Thursday night, in Piazza Mignanelli, in the shadow of the Spanish Steps.

Others designers presenting their fall-winter collections include Andre Laug, Barocco, Galitzine, Mila Schoen and Lancetti.

The shows end Friday night.