The Carter administration yesterday completed its briefings of Congress on Cuba's alleged role in the invasion of Zaire, but its effort failed to resolve the controversy about whether the evidence proves Cuba helped the invading forces.

That became clear after Central Intelligence Agency Director Stansfield Turner met with the Senate Foreign Relations Committee in a three-hour closed session to describe the reasons for President Carter's charge that Cuba helped train and equip the rebel invaders.

It was Turner's fourth appearance before a congressional committee this week. As was the case with his other briefings, his presentation yesterday drew sharply mixed reactions from those senators who heard him.

Those who have tended to support Carter said Turner had convinced them that the president's charges were correct. But those who have questioned the accuracy of the evidence said they still have heard nothing to put their doubts to rest.

Sen. George McGovern (D-S.D.), who originated the committee's request for the administration's evidence, summed up the situation by saying:

"There's a definite parallel with what happened during the Vietnam war. Different people look at the same data and draw different conclusions from it."

McGovern, who has been the most vocal of the doubters, added that he was still unconvinced after hearing Turner and examining the evidence. He said: "While they may have enough circumstantial evidence to bring in a rather shaky indictment against the Cubans, they would never get a conviction based on the evidence they have."

Even committee Chairman John J. Sparkman (D-Ala.), a staunch administration loyalist on most issues, reacted cautiously. He said, "The weight of the evidence is circumstantial, and that weight is substantial but by no means conclusive."

Similar caution was expressed by such key committee members as Sen. Frank Church (D-Idaho), who is in line to become committee chairman next year, and Sen. Dick Clark (D-Iowa), who heads the subcommittee on Africa. Both said they wanted to take closer and harder looks at the evidence before making up their minds.

Of those senators willing to comment on Turner's presentation, the strongest support for the administration came from Sen. Jacob K. Javits (R-N.Y.). "The president has not conjured up some incident to discredit the Cubans," Javits said, but he added that he was unwilling to characterize the degree and depth of Cuban involvement in the Zaire situation.

Although the reactions yesterday were the most skeptical and reserved that Turner has encountered in his forays up to Capitol Hill this week, the administration has been encountering questions about its charges ever since Carter first made them in a Chicago press conference on May 25.

The president said specifically that the rebels who invaded Zaire's Shaba Province from the neighboring Marxist state of Angola were trained and equipped by the Cubans. He also charged that Cuba knew of the invasion plan and did nothing to stop it.

President Fidel Castro's government has denied these charges. It has admitted helping train Angola-based rebel foes of Zaire President Mobuto Sese Seko in the past, but has insisted it played no role in last month's invasion.

The ensuing argument about whether Castro or Carter is correct has centered on two points: Whether the intelligence on which the administration based its charges comes from reliable sources and whether it establishes a recent connection between the Cubans and the rebels.

Those who have seen the evidence say part of it involves satellite photos that allegedly show Cuban camps located near rebel camps in northern Angola and a Cuban ship unloading supplies at an Angolan port.

But, as has become clear during the past week, the overwhelming mass of the administration's evidence consists of reports collected by the CIA from African diplomats, from captured rebels and from agents of other governments.

The CIA, which refuses to identify its sources, insists that its intelligence adds up to a "preponderance of evidence" about Cuban involvement.

However, many sources, including some administration officials who ask not to be identified, say that much of this intelligence was obtained second or third hand or comes from sources of doubtful reliability. As a result, the sources contend, the evidence is too circumstantial and too susceptible to differing interpretations to be conclusive.

On the second point - whether Cuba can be tied to last month's invasion - Turner told reporters yesterday that the evidence proves Cuba trained and equipped the rebels "over several years" including the period between a rebel attack on Zaire in March 1977 and last month's operation.

However, that charge also is disputed by many who have seen or been briefed on the evidence. McGovern, for example, said yesterday he had no doubt that Cuba has helped the rebels in the past, but added he had seen "no hard evidence" to connect Cuba with the latest invasion.

When reporters questioned Turner on these points, he replied that "intelligence is not court procedure evidence. The job of intelligence is collecting many little pieces and clues and fitting them into one picture. We have many, many pieces of evidence in this situation. The cumulative effect is persuasive."

In fact, Turner insisted, the evidence is so strong that he did not see how "reasonable men" could look at it and not be convinced that "Cuba has to bear responsibility."

So far, the evidence has been made available only to Congress on a highly restricted basis to guard against unauthorized disclosure, and administration sources say they do not intend to make any of it public.

In that, the administration even won the backing of McGovern, who said he didn't believe the information could be classified without revealing the CIA's sources and methods of collecting information.

Administration sources concede this exposes them to possible charges of a "credibility gap." However, they add, the White House has decided to take that risk and hope either that a majority of Congress and public opinion will accept the administration's word or that the controversy simply will blow over and be forgotten in a short time.