ROME, JULY 2 -- With a carnival atmosphere that reflected the nation's continuing political confusion, Italy opened its new political season today with the official inaugural of its 10th postwar Parliament.

Although the first session of the recently elected Senate and Chamber of Deputies was held for the normally staid business of electing chamber presidents, public interest focused more on the seating in Parliament of a blonde porno star than on the posturing of Italy's leading politicians.

To the surprise -- and relief -- of almost everyone, the Hungarian-born porn queen, Ilona Staller, better known by her stage name, Cicciolina (little fleshy one), was uncharacteristically demure as she took her seat in the Chamber as one of 13 Radical Party deputies.

While in her political campaign she dressed in white with X-rated decolletage, often baring her chest to the cameras, Staller showed up today dressed conservatively in green, her dress reaching up to her neck and her arms sheathed.

Staller, 37, who surprised everyone, including the Radicals, by winning a seat in Parliament, did manage to steal the show in the traditional parade of arriving politicos at Parliament's Piazza Montecitorio today.

As about 300 spectators cheered and laughed behind police barriers, Cicciolina arrived amid a demonstration of 50 followers, including four other porno stars from her night club act.

As her fans shook signs shaped like giant lips that read "Welcome to Parliament," Cicciolina was mobbed by photographers and reporters until parliamentary security guards whisked her into the chamber.

"This is all very amusing," said the new deputy who before her election was better known for her naked, on-stage wrestling matches with a python.

She had been put forth as a candidate by the Radical Party as an act of ridicule of the Parliament. The party clearly expected her to be defeated; instead she polled the party's second-highest vote.

Her entry into Italian parliamentary democracy was quickly followed by more of the sort of street political theater that is common in Italy.

A group of angry tenants demonstrated against what they called the scandal of Italy's rent laws and lack of reasonably priced apartments. Next to them a group of jeans-clad young fascists shouted at the assembling legislators to free Paolo Signorelli, the jailed ideologue of the extreme right.

From the balcony of the Chamber, seven deputies from the ultraleft Proletarian Democracy Party hung a 20-foot banner calling for a national referendum against nuclear energy.

Inside the two chambers, however, the politicians reigned.

In the Senate, Republican Party leader Giovanni Spadolini, 62, prime minister in 1981-82, was overwhelmingly elected president of that chamber. Leonilde Iotti, 67, a Communist, was reelected to head the Chamber of Deputies, as she has in the two previous legislatures.

The elections came as no surprise. They had been agreed to last night in a meeting of the parliamentary leaders of the five parties that made up the coalition government that ruled Italy from 1983 until this spring.

This agreement, however, was not taken to mean that the dispute between the Christian Democrats and the Socialists that had broken up the old coalition was on the verge of being resolved.

The real struggle to give Italy a new government has yet to begin. So far neither Christian Democratic leader Ciriaco de Mita nor Socialist leader Bettino Craxi has shown any willingness to end their dispute over which party should control the prime ministership.

Craxi's 3 1/2-year rule collapsed in April when de Mita insisted that he step down and allow a Christian Democrat to be named prime minister, since the Christian Democrats were by far the largest party in the coalition. Besides the Socialists and Christian Democrats, the old coalition included Spadolini's Republicans, the Social Democrats and the Liberals.

The political jockeying will begin in earnest next week when President Francesco Cossiga begins consulting parliamentary and party leaders before designating a political leader to try to form a new government.

In view of the continuing confusion from the Craxi-de Mita feud, hopes are not high here that an agreement will be reached quickly and most political pundits predict that it will take a long time before a stable government can be formed.