Egypt sewed a new patch on the crazy quilt of African alliances and rivalries today by alleging that Libya has begun trans-shipping Soviet weapons to the embattled Marxist government in Ethiopia.

Reports in the Cairo press that had every sign of being officially inspired said that Libyan planes are ferrying the weapons, including surface-to-air missiles, to Ethiopia by way of Niger and Cameroon in West Africa. That is a circuitous route, but it makes sense in the kaleidoscope of north and east Africa, where Libyan planes headed for Ethiopia would not be welcome to pass over the countries on the direct route, Chad and Sudan.

There was no independent confirmation of the Egyptian report and it apparently took Western military analysts here by surprise. They said they could not confirm a related report that Libya's port of Benghazi has been closed to normal commercial traffic for a week while new shipments of Soviet arms are unloaded there.

The Soviets have been supplying weapons to Ethiopia since it renounced the U.S.-Ethiopian military assistance agreement last year. But the Soviets have also equipped their old client, Somalia, which is now involved in an armed struggle with Addis Ababa in Ethiopia's Ogaden region.

Why the Soviet Union would ship weapons to Ethiopia by the cumbersome Libyan connection instead of directly to Ethiopia's own ports is not clear, and calls into question the credibility of the whole story. One possibility raised by analysts here is that the Ethiopian government no longer feels secure enough in its control over the roads from these ports, threatened by insurgents in the Red Sea providence of Eritera, to risk bringing in vital weapons by that route.

Another possibility is that Moscow is trying to conceal the extent of its aid to Ethiopia from the Somali's.

The Egyptian reports said the Libyan leader, Col. Muammar Qaddafi, was anxious to help the Ethiopians shore up their defense of the city of Harrar, in Eastern Ethiopia. Harrar has been threatened by Somali-backed invaders seeking to wrest the Ogaden region from the control of Addis Ababa and make it part of Somalia.

It has been well established that massive amounts of Soviet weaponry have been pouring into Libya, over the past two years, much to the concern of the Egyptians, who fought a brief border war with Libya in July and consider Qaddaffi an agent of Soviet expansionism.

Foreign military analysts have expressed the belief, however, that most of the weapons were staying in the hands of the Libyan armed forces, which are thought to have far more weapons than they are capable of using. Libyan trans-shipment of Soviet arm to other parts of Africa would be a new development.

After a visit to Libya by Cuban President Fidel Castro earlier this year, diplomatic analysts said it was likely that the radical, pro-Soviet Qaddafi was prepared to assist the Ethiopians if he could. Castro went to Ethiopia after Libya.

Ethiopia and Libya are joined by their common hostility to the moderate, anti-Soviet governments in Egypt and Sudan.

Egyptian reports of events in Libya are inaccurate as often as not. But true or not, the latest one reflects Egypt's deep anxiety over the Soviet foothold in Libya and the radicalization of Ethiopia. Egyptian President Anwar Sadat has openly accused the Soviet Union of seeking to take over Africa and of trying to undermine his rule, through its arms shipments to leftist governments and its support of radical movements.

Egyptian hostility to Ethiopia is compounded by the widespread Arab belief that Ethiopia is a league with Israel, accepting Israeli military training in exchange for air facilities on the Red Sea. This has been denied by Israel, but a columnist in the influential newspaper Al Ahram warned this morning of the "Israeli-Soviet Dagger" aimed at Egypt and Sudan from Ethiopia.