ROME (AP) _ Early projections indicated the Christian Democrats, who led or dominated every Italian government since World War II, were holding their own today in parliamentary elections, with the Communists suffering a big setback.

The projections broadcast on state-run RAI television had former Premier Bettino Craxi's Socialists might make gains, but below party hopes.

The projections were for the 315 seats in the Senate. The Doxa polling organization said it would give projections for the 630-seat Chamber of Deputies later.

The elections Sunday and today are to lead to the formation of Italy's 47th postwar government. No party was expected to win an outright majority. But the percentage of votes each party gets will affect the leverage it has in forming the next coalition.

The polling company said the long-dominant Christian Democrats were figured to receive 32.4 percent of the vote, the same as in the last elections for the Senate in 1983.

The projections showed the Communists, Italy's second largest party and the biggest Communist party in the West, slipping from 30.8 percent in 1983 to 27.3 percent.

The Socialists, who polled 11.4 percent in 1983, will receive 11.0 percent, the projections indicated.

That figure, however, does not include votes going to an alliance of Socialists, Social Democrats and Radicals running in five regions. Those votes, projected at 3.4 percent, will eventually be split among the three parties under Italy's complicated proportional representation system.

The rest of the votes are scattered among smaller parties, including the Greens, who were projected to get 2.2 percent in their first parliamentary bid.

The elections were called a year early after a two-month political crisis that began in March when Craxi stepped down over a dispute with the Christian Democrats in his coalition.

A caretaker government led by Christian Democrat Premier Amintore Fanfani is overseeing the elections.

Communist leaders today blamed their election losses on votes that went to the Greens, who ran on an anti-nuclear and pro-ecology platform.

''There was an erosion in our electorate toward the Greens,'' Communist Sen. Emanuele Macaluso told reporters at party headquarters. ''It was a protest vote.''

In general, the projections showed a stability of votes for the left, but a splintering among the various leftist parties.

The two-day elections generated few issues, but plenty of polemics.

Turnout was put at over 80 percent.

Doxa said the projections, based on 309 of 600 sample precincts, had a maximum margin of error of 1 percent.

A voter must be 21 to ballot for a senatorial candidate. Voting age for the Chamber of Deputies is 18, making the Senate projections slightly less representative.

Polls were open today from 7 a.m. to 2 p.m. More than two-thirds of the eligible voters cast their ballots Sunday.

Craxi's coalition included the Christian Democrats, the Socialists, the Social Democrats, the Liberals and the Republicans.

There were 45.6 million Italians eligible to vote for deputies, while 39 million were eligible to vote for senators.

Newspaper editorials blamed the apparent apathy of voters on a lengthy campaign that featured a lot of mud-slinging, but little debate on substantive issues.

Pornography star Ilona ''Cicciolina'' Staller, a candidate for the Chamber of Deputies on the small Radical Party ticket, provided one of the most startling moments in the election.

As she cast her vote in Rome, she pulled her white halter top down to bare a breast for photographers and television cameras, prompting an election worker to try to cover her with a sheet of paper.