Who do the Cubans think they are? Americans? They go rampaging around the world as if, like the United States, they had a "Manifest Destiny." Insufferable! No wonder President Carter is outraged.

After all, who empowered Castro to usurp America's established role as policeman of the world? Imitation may be the sincerest form of flattery, but even so, as Jimmy Carter says, there's a limit.

Take Africa, for example. According to the CIA, Cuba has 12,000, or 17,000 or 25,000 men in Ethiopia. What are they doing there? Well, in their impertinent way, they reply by asking what 40,000 U.S. troops are doing in South Korea.

Our answer is that we were invited in, and we are still there to guard against a potential invasion by North Korea. Also, if we suddenly pulled out, South Korea's military dictatorship might be overthrown by dissidents who want to establish a democratic government.

Castro tries to counter this by insisting that Cuba likewise was invited in by the Ethiopians to help them defend themselves against an actual invasion by neighboring Somalia. What red-blooded American is going to believe that, even if it is true?

Cuba, like the rest of the world, ought to realize by now that the United States in principle is against foreign military or para-military interventions, although, of course, there are times when a great power must rise above principle, as in our Bay of Pigs invasion, of Cuba in 1961.

As every fair-minded person knows, however, we did this only for Cuba's own good, so there is no call for Castro treating this as a precedent for intruding in other countries like, for instance, Angola, where three rival liberation groups (or tribes) fought for power after the colonial Portuguese government collapsed.

Not even the boastful Castro can claim he got to Angola ahead of us. Although the United States never gave up on the Portuguese until the end, we for years took out insurance by secretly giving aid to Holden Roberto and his ineffectual National Front for the Liberation of Angola.

Later, after the Portuguese fled, the CIA also covertly supported Joseph Savimba and his National Union for the Total Independence of Angola, which got help, too, from President Mobutu of Zaire and from the whites of South Africa, which did not endear us to the continent's blacks.

Meanwhile, the Russians had for years been supporting the Popular Movement for the Liberation of Angola headed by Agostinho Neto, who now heads up the Angolan government in Luanda after winning the civil war with the help of Cuban troops who poured in when the CIA stepped up its campaign.

In short, Castro beat the United States at its own game, which is intolerable enough, but now he claims his forces are "stabilizing" Angola, and he doesn't even give Andrew Young, our U.N. ambassador, credit for saying it first. It's rank plagiarism.

Congress has just heard expert testimony that Cuban support recently helped Neto put down an internal challenge by a radical dissident faction backed by Moscow. Moreover, Castro's men are safeguarding the Gulf Oil installation at Cabinda which, with the blessing of Neto, continues to flourish as the country's largest private enterprise.

In any case, "stabilization" is a speciality of the United States. We made it famous in 1965 when we invaded the Dominican Republic at the time a military coup overthrew the democratic government of Juan Bosch. Like the Cubans in Angola, our troops stayed on for some time, and they stabilized the country so well that the leader of the coup has been in power ever since, although he has just lost an election - which the military almost upset.

If the Cubans have to imitate us, why can't they pay attention to what we preach instead of what we practice? Our Monroe Doctrine, for example, strictly forbids foreign interventions anywhere in the Western Hemisphere, and, as the Russians can testify after the Cuban missile crisis, we mean it - with one exception.

Since the turn of the century, we have reserved for ourselves the exclusive right to guide our often misguided neighbors into the path of U.S. righteousness and, if necessary, to send in the Marines or the CIA or both to make sure that Cuba, Chile, Mexico, Haiti, Nicaragua, Panama and Guatemala, among others, got the point. But how much gratitude have we got for it?

For a small island with only 9 million people, Cuba has been making quite a dent internationally. Nonetheless, Castro is suffering from delusions of grandeur if he thinks Pax Cuba can match or top Pax Americana. "It is time," says Henry Kissinger, "that one overcomes the ridiculous myth of the invincible Cubans." But he failed to note that the myth flourishes only in the United States, chiefly in the White House. However, the Chancellor of West Germany, Helmut Schmidt, didn't miss the point. He says: "It would be strange indeed if the United States with 220 million people should be hypnotized by Cuban military adventures on another continent."