President Samora Machel of Mozambique has congratulated the Reagan administration for imposing limited sanctions on South Africa and has called upon it to take "further steps" to pressure the white government there into ending apartheid.

"We did congratuate the Reagan administration for these steps already taken," he said in an interview with editors and reporters of The Washington Post a day after his two-hour meeting Thursday with President Reagan.

"This is a first step, and the first step is always important," Machel said. But he quickly added that the administration should quickly "consolidate" its initial sanctions "so that it can decide upon what further steps ought to be taken, and the American government knows it."

"We said the American administration should increase the pressure to eliminate apartheid," he added, apparently referring to his conversations with top administration officials during his four-day visit here.

Machel gave no hint that Mozambique is opposed to economic sanctions, even though the South African government has argued that they would hurt its African neighbors like Mozambique far more than South Africa itself.

The Mozambican leader seemed more concerned about the fate of the Nkomati accord, which he signed with South Africa in March 1984 in a bid to lessen tensions in the region and establish better relations with its government. The accord called for South Africa to end its support for the Machel government's main internal opposition, the Mozambique Resistance Movement (Renamo). In return, Machel agreed to halt African nationalist guerrillas' raids from Mozambique into South Africa.

A senior administration official earlier this week cited the Nkomati agreement as "a major milestone" in U.S. efforts to promote detente and better relations between white-ruled South Africa and its black African neighbors to the north. Now, however, the fate of the agreement -- and of Mozambican-South African relations as a whole -- appears very much in doubt.

On Monday, Mozambique presented the South African government with evidence that it has broken its pledge not to provide arms and other forms of aid to Renamo. South Africa has since admitted its aid to Renamo was continuing but charged Mozambique was still helping South African nationalist guerrillas.

Machel carefully avoided saying what his government planned to do in response to the South African violations or how he thought they would affect the Nkomati accord. Instead, he blasted past South African support first for colonial Portugal against the nationalist guerrilla struggle in his country and then for the whites of Rhodesia (now know as Zimbabwe) against black nationalists there.

He charged that many Western countries are also aiding the Renamo guerrillas and that there is "an international conspiracy" against Mozambique. However, he said the United States has always supported the Nkomati accord and "never been ambiguous" in its relations with his government.

Asked whether there is any possibility of a reconciliation between his government and Renamo, as South Africa has sought, Machel expressed outrage at the idea. "There can be no possible reconciliation with bandits and terrorists," he said, adding that the United States has never asked him to negotiate with Renamo.

Machel's visit was protested by conservative lawmakers and groups because of his strong Marxist convictions and his government's close relations with the Soviet Union, which has provided most of Mozambique's arms since its independence from Portugal in 1975.

Asked about his ties to the Soviet bloc, the Mozambican leader said his country is "African, independent and nonaligned," adding that, "there is no question of blocs. We don't belong to either."

As to whether he is still a Marxist and sticking to his socialist economic policies after a decade of extreme economic difficulties, Machel avoided a direct answer. Saying that Marxism is neither a "dogmatism" or a "religion," he added that it is a good tool for analyzing problems to find "the truth."