Rhodesian Prime Minister Ian Smith, rebuffed by the Carter administration, yesterday won some important words of sympathy from former secretary of state Henry A. Kissinger for Smith's plan to move Rhodesia to majority black rule.

Kissinger's support, although qualified, still put him at odds with the Carter administration on a major foreign policy issue for the first time since he left office two years ago.

His stance represented a considerable victory for Smith, who is in the United States desperately seeking American support for his embattled government. So far, Kissinger is the only voice in the U.S. foreign policy arena to say a kind word in his behalf.

After meeting with Smith, Kissinger told reporters that Smith appears to be trying to move toward free elections for all Rhodesians with his so-called "internal settlement" plan, and added: "I think we should test that process.'

"I'm saying we should support the internal settlement," Kissinger specified carefully. "I'm saying we should give his approach an opportunity."

That was in marked contrast to the position taken by Secretary of State Cyrus R. Vance in a meeting with Smith Monday. He reiterated the Carter administration's belief that Smith's plan is inadequate to resolve the strife between Rhodesia's black majority and while minority.

Under the internal settlement, Smith, in association with three black Rhodesian leaders, has set up a transitional government he contends will pave the way for elections resulting in the country's first black government. These elections are supposed to take place in December, although Smith says technical difficulties may force their postponement for several months.

The Carter administration has refused to endorse Smith's plan because it lacks the support and paticipation of the Patriotic Frong guerrilla forces fighting against Smith's government from bases outside Rhodesia.

Washington has been pressing for a peace conference of all the parties to work out a cease-fire adn a power-sharing agreement that will bring the Patriotic Front into the process of moving toward elections. So far, though, Smith and the front's leaders, Joshua Nkomo and Robert Mugabe, have refused to deal with each other.

Kissinger said yesterday that, he too, favors an all-parties conference. But he parted company with the administration by agreeing with Smith's contention that U.S. refusal to give Smith any support encourages the guerillas to shun negotiation and keep on fighting.

In a reference to the military aid given to the Patriotic Front by communist countries, Kissinger said: "I don't believe that, just because they have Cuban and Soviet arms, they should be able to set our policy."

Kissinger's position appeared to stem from his effort, while serving as secretary of state two years ago, to work out a Rhodesian solution. In his public appearances here, Smith has said several times that Kissinger promised him U.S. support if Smith would move Rhodesia toward one-man, one-vote rule.

Smith has asserted further that he adopted his internal settlement plan in response to that assurance. But, he contends, the Carter administration has failed to live up to that bargain.

Both Kissinger and the State Department deny that Smith was given any explicit commitment. Instead, they say, the bargain suggested by Kissinger was to try to get the agreement of the other parties to accept Smith's commiment to the principles of majority rule.

However, negotiations broke down, and State Department contends that the failure of all he contesting paries to agree on a plan for majority rule nullified Kissinger's proposals.

In his remarks yesterday, Kissinger glossed over that period, saying "conditions have changed" since his 1976 peacemaking effort. But he added:

"The issue for the United States is whether we should support a transition through the ballot or support people who want to fight their way in through bullets. In principle, I think the United States should support a solution based on elections.

"What I had in mind," he added, in reference to his 1976 mission, "was a solution based on free elections that would protect the rights of all citizens of all races. That's what they [the Smith government] say they want. I think we should test that process."

Also yesterday, Smith, in a meeting with some members of the Senate Foreign Relations Committee, said he is willing to meet the Patriotic Front leaders in an all-parties conference with "absolutely no preconditions." His objection, he added, was to what he called U.S. and Bristish "preconditions" about first dismanting the Rhodesian security forces and imposing a British high commissioner over the breakaway former British colony.

Smith also said that, when the elections called for by his plan take place, he will welcome observers from the United Nations. "The more the better," he said.