A U.N. committee today side-stepped a controversial Cuban resolution demanding independence for Puerto Rico by voting to adjourn for a year.

The decision by the Special Committee on Decolonization represented a notable victory for the United States. Despite signs of changing attitudes in Puerto Rico, the United States maintains that the issue does not fall within U.N. jurisdiction.

Diplomats here believe that the Cuban resolution probably would have passed if it had been allowed to come to a vote. Instead, a comfortable majority of the "Committee of 24" went along with an Australian motion to adjourn: Eleven in favor and seven against with four abstentions and two absent. The United States is not a committee member but has been quietly lobbying for adjournment.

The committee's decision gives the Carter administration and Puerto Rican leaders a breathing space in which to reassess the island's present commonwealth status.

This year, for the first time, virtually all shades of Puerto Rican political opinion came to New York to address the committee's earlier session, Aug. 15 to 17. In the past, only the tiny pro-independence groups has turned up.

Despite their disagreements on all other issues, all speakers agreed this year that the island's current relationship with the United States contains at least vestiges of "colonialism." The Australian delegate today referred to this unusually varied range of viewpoints, calling it "only one of many indications that the situation in Puerto Rico continues to evolve."

But, he went on. Puerto Ricans have the opportunity to choose their own future. On the other hand, he added, the Cuban resolution implicity involves the United Nations in Puerto Rican affairs and is not justified. A one-year adjournment would not prejudice the evolution of the island's situation, he added.

In an effort to broaden the appeal of their resolution, the Cubans had very slightly softened its tone. But its overall thrust remained anathema to the Americans.

Terming Puerto Rico a "colonial situation," the resolution demanded that immediate steps be taken to enable Puerto Ricans to exercise the right to independence. It urged all parties to refrain from any action that might influence the outcome, including "the exploitation of the mineral and energy resources of Puerto Rico." And it called for the release of Puerto Rican "political prisoners" - a reference, the Cuban delegate explained, to the five nationalists jailed in the United States even since an assassination attempt on President Truman and an armed attack on Congress in the 1960s.

The biggest surprise of the August committee session was the appearance here of two leading representatives of the Popular Democrats, the main opposition party. It was a major switch even though the two men made it clear that they opposed any U.N. jurisdiction and were present in their private capacity. The Popular Democratic Party, which favors a modified commonwealth status, was the island's ruling party until last November's election.