Andrew Young, the U.S. ambassador to the United Nations, pointedly separated himself from the State Department again today, this time over Cuban military advisers in Ethiopia.

Young told an informal press conference he did not share the "grave concern" he attributed to the department because "maybe the Cubans might be a little more rational than the Ethiopians at this point."

The Ethiopians, he said, "are killing people right and left, and I guess I think maybe and the Cubans might be a little more rational than the Ethiopians at this point. It depends on what they advise."

On Wednesday the State Department confirmed a Washington Post report that 50 Cuban military advisers are in Ethiopia and that there were rumors that they are the vanguard for 400 to 500 more Cubans expected in Ethiopia over the next few weeks. A department spokesman said that if the additional Cubans were sent it "could be serious development."

[Young was asked after his arrival at Andrews Air Force base Thursday what the effect of another 400 to 500 Cubans might mean in Ethiopia. "If they are killing more people, then that's just terrible," he said. "If they are going to help stop the killing, then that is good."]

The Ethiopian government is fighting several different separatist movements as well as carrying out an internal purge that has reportedly taken the lives of uncounted thousands.

Earlier this year, Young found himself on the other side of the fence from the State Department when he called the Cuban troops in Angola a "stabilizing influence" there.

Young's characteristic outspokenness, an aide explained privately, meets with the approval of President Carter. Like President Franklin Roosevelt, the aide said, President Carter welcomes administration voices that seemingly conflict. One set, the aide explained, expresses the formal position - "concern" in this case - and another reflects how the President and his Secretary of State really view a problem.

In effect, then, young would be signaling that Cuban behavior in Ethiopia will determine the administration's judgement.

President Carter was asked at his press conference Thursday whether he was not applying a doubel standard in transfering Gen. John K. Sinpplying a double standard in transfering Gen. John K. Sin policy while permitting Ambassador Young to express his dissent. Carter answered, "I know of no instance that Andy Young has violate a policy you described."

Vice President Walter Mondale said Thursday that "it's hard to disagree" with Young's comment that the Cubans might be more rational than the government in Addis Ababa. "That isn't saying much, of course, because that's been a very militant, even violent government of Ethiopia," he said in an appearance on NBC-TV's Today show.

On other topics, Young explained why he repeatedly and publicly points to racism in Britain.

It began, he said, with a BBC reporter who "was taunting me, saying that the U.S. was the only one that had any race problems . . . I think it is a pervasive problem . . . There are problems of culture and racial difference all over the world."

(Sweden's ambassador to the United Nations, Anders Thornborg, has asked the U.S. mission for an explaination of Young's remark on Wednedsay that "the Swedes are terrible racists," Reuter reported from the United Nations.)

Young has just finished an African tour and stopped over here to refuel. Asked if he "exploited" his own blackness in southern Africa, he replied easily:

"A little bit but not much. There is no way I can't identify with the blacks, but actually I spent far more time with the whites because I think they have the problem."

He stressed that he had thought "violence was totally unacceptable" in South Africa" and I discourgaed violence at every opportunity." There were, he added "all kinds of tactical reasons that make violence just impossible," presumably a reference to the police power of the white state.

But in Rhodesia and Namibia, "where things have gone much further, there is a completely different situation," Young said, a reference to his refusal to condemn violence there "I didn't feel as though I could take the moral authority of telling people what to do about their independence."

[TEXT OMITTED FROM SOURCE] since the embargo began, according to diplomats here.

[A copy of the agreement released in Washington said that Cubans ships with fishing licenses will be able to center the ports of New York, Boston and Philadelphia. Permission to call at other ports can be arranged later.]

Under the fishing agreement signed here last month and made public by the magazine Bohemia yesterday, the two countries will also cooperate in scentific research onfishing resources.

The agreement, which followed the first direct official talks betwen the countries in 16 years, was part of a recent improvement in relations that included vists by American legislators and businessmen.

It sets out the line between Cuban and American fishing zones and gives Cuban vessels some right of access to the areas within the U.S. zone. The United States will determine allowable catches in its zone each year and issue licenses for Cuban vessels to fish inside it.