The powerful Italian Communist Party today wound up a week-long critical examination of the party's recent unprecedented electoral losses with a sweeping reorganization of its two top executives bodies.

The shakeup of the West's largest Marxist party was considered a striking victory for Party Secretary Enrico Berlinguer, who, despite the party's severe losses in the June 3 national election, is clearly capable of marshaling vast support among party officials for his long-range policy of compromise with Italy's Catholics.

Berlinguer apparently believes that although the party made some tactical erros in recent months, its basic policy of seeking membership in a broad national coalition is essentially "valid and correct."

Five ranking members of the party's nine-man Secretariat were replaced, and the size of the Secretariat was reduced to seven. Ten members of the party's Directorate or Politburo also were removed from office, and its size was reduced from 36 to 32.

Those removed from the Secretariat and Politburo today included the heads of the press and propaganda, organizational, and television sectors. Also removed from the Secratariat were two veteran leaders, Giancarlo Pajetta, who recently has been critical of Berlinguer's position, and Paulo Bufalini, who is considered too conservative.

The cut in the size of the Secretariat, two of whose seven members are in charge of purely technical matters, further increases Berlinguer's status.

"One could say that Berlinguer is now the center forward on the five-man attack squad of our soccer team," one Berlinguer supporter said.

In last month's election, the Communists suffered their first losses at the polls here since 1946, winning only 30.4 percent of the vote compared to the 34.4 percent polled three years ago. The losses cost the party 26 seats in the Italian Chamber of Deputies.

The disappointing results gave rise to widespread criticism among party militants and leaders, as well as the rank and file. Much of this criticism has been directed at the party's 2 1/2-year policy of providing essential parliamentary support for a minority government of the ruling Christian Democrats. The Communist Party ended that support last January, and no party has been able to form a workable coalition since.

Some of these critics have charged that the party was so involved with high-level political maneuvering in Rome that it lost touch with its voters, many of who this year voted for single-issue radicals or for small, far-left parties.

Others believe that the party's mistake has been to seek an alliance with the centrist and often conservative Christian Democrats rather than to seek an alliance with the Italian Socialists and Italy's other leftist groups.

In his 76-page address to the Central Committee last week, Berlinguer recognized that too little attention had been paid to the concrete interests of the rank and file, Italian youth and the country's poor. He admitted that the party had developed a somewhat bureaucratic mentality.

But he used international and domestic considerations to rule out the possibility of a future left-wing government coalition here and at the same time scoffed at those Italians who would like to see the Communist Party become a genuine social democratic force.

Berlinguer demonstrated support for the party's decision to return to the opposition and to deny backing to any government that refuses to give the Communists Cabinet posts.

Last week's Central Committee meeting was one of the most open that observers here can remember. Although in the end of the party closed ranks around Berlinguer, it was clear that conflict and debate over future policy can no longer be stifled.