Prime Minister Ian Smith said here today that he intends to run in April for a seat in Rhodesia's first parliament with a black majority and will not retire from politics until the new government gains international recognition.

In an interview, Rhodesia's white leader said, "Sure, I'm going to run," although he was still "absolutely genuine" about retiring once the West recognized the new government and economic sanctions against his country were lifted.

This startling revelation of the aging Smith's intention to continue playing a prominent role in Rhodesian politics came as surprising news to one of Smith's black colleagues in the biracial transitional government's ruling Executive Council.

"The Africans will be shocked by that," the Rev. Ndabaningi Sithole said in a separate interview shortly afterward. "They will say, 'What is this?'" he added.

"We've been told by moderate black states and Western countries, and Mr. Smith is aware himself, that he is a great hindrance to our recognition," Sithole said.

"The very physical presence of Mr. Smith in the new government reduces the possibility of getting recognition and settling the problem.... The sooner he leaves the better it will be for the country," the black leader said.

Smith, 59, had said earlier that he did not plan to run in the April elections and would retire to his farm at Selukwe in central Rhodesia.

Provided he wins a seat in the new Parliament, the prime minister is certain to be appointed a key minister in the Cabinet since whites are guaranteed at least five ministerial positions under the new constitution.

Because Smith stands as the symbol of white minority rule in Rhodesia, his presence in the black-led government is bound to be interpreted in black Africa as a clear indication that there has not been a genuine transfer to black majority rule. This would make it unlikely that enen moderate African states would recognize the new pro-Western government.

Even officials of Smith's closest ally, the South African government, have been indicating in private conversations that it would be far better if he stepped down as soon as possible to improve the embattled government's chances of gaining Western support in the face of mounting guerrilla opposition.

"We feel his usefulness is over," said one South African foreign affairs official, now that Rhodesian whites, in their referendum Jan. 30, approved the new constitution for black majority rule.

Sithole said, "It was my understanding that after the constitution became the law of the land in the first week of March, Smith would resign."

Smith made his surprise disclosure during a wide-ranging, hour-long interview. He said that although the transitional government would try to get more than 50 percent of the country's 2.8 million voters to cast their ballots, the worsening war situation might make it impossible to get more than 20 percent of the qualified voters to the polls.

Smith pleaded for Western understanding of the difficulties facing the government in holding the election because of what he called mounting intimidation by nationalist guerrillas.

"I would have thought that if in the end we only got 20 percent, bearing in mind we were doing our utmost and that the only people who were frustrating the election were Marxist terrorists with guns, then the free world would be sympathetic to a result such as 20 percent," he said.

The prime minister said he was buoyed by what he saw as an upswell of U.S. congressional support for Rhodesia's effort to bring black majority rule to the former British colony since the fall elections in the United States.

The Rhodesian white leader said he was "doubtful" that a Western peace conference could be arranged before the April 20 elections and he accused the British and American governments of "deliberately resorting to delaying tactics" in not calling one. Smith would not clearly commit himself on the issue of whether he would call off the elections if a conference could be convened.

"But at the moment," he said, "we are getting along with our elections because we don't believe the U.S. and British governments have any intention of calling a conference. Anything they say to the contrary is bluff."

Smith also did not rule out the possibility of another secret meeting with black nationalist guerrilla leader Joshua Nkomo, who is based in neighboring Zambia.

"I've said I will always meet anyone and go anywhere in this world to meet anyone, provided it is in the interest of my country, but I cannot tell you if this thing is in the offing now," Smith said. Nkomo is the leader of the Zimbabwe African People's Union, one of the guerrilla groups fighting to bring down the Salisbury government.

Smith said he was not really changing his position regarding his plans to retire from politics, but that he had been "impressed" by the number of whites who had asked him to stay on until the new black-run government is firmly established.

"I'm going to stick by what I've always said -- that I want to retire from politics and this is absolutely genuine. I want to impress that upon you," he said, adding that after 30 years in politics, 15 of them as prime minister, he had had enough.

"But I have said all along that my retirement is contingent upon a completion of this operation which I started... to get our recognition. It looks as though we are nearly there now," he added.

Asked if this meant that he intended to be in politics for the next five years -- the life of the new Parliament -- Smith replied, "No. If we get recognition and removal of sanctions, then I will be out... I believe I would retire. I would hope within hours."