Mozambican President Samora Machel opened a special conference of 25 non-aligned nations here today with a blistering attack on the Western powers for their policies toward the three remaining white-ruled nations of southern Africa and accused Rhodesia of seeking to plunge the entire region into war.

Machel also attacked the United States, without mentioning it by name, for bolstering its nuclear naval strength in the Indian Ocean in connection with the Iranian crisis and said the "growing imperialist military presence" there was aimed at intimidating Mozambique and all other nations in the region.

Machel also accused the West of maneuvering through various plans for a peraceful settlement of the disputes in Rhodesia and Namibia to insure the survival of their own economic and political interests and split the guerrilla movements away from the socialist countries which were providing them with all their arms.

He said armed struggle was now the only way left to achieve "true independence" in Rhodesia and that any future negotiations would have to take in account "the realities and victories" obtained by the nationalist guerrillas on the battlefield.

Machel was speaking at the opening of a special conference on southern Africa being attended by the foreign ministers from the 25 nations represented on the coordinating bureau of the nonaligned group. It is in preparation for the nonaligned summit in Havana this summer.