Soviet arms are pouring into Ethiopia at such a rate that the capital's international airport was swamped this week with Soviet military aircraft, forcing scheduled civilian airliners to bypass Ethiopia, diplomatic sources said today.

The sources said that at one point there were at least 16 crated Mig fighters at the airport. They were probably Mig-12s, although there have been unconfirmed reports that Moscow has also sent some of the sophisticated Mig-23s, the Soviet Union's main fighter plane.

The p Soviets have been pouring hundreds of millions of dollars worth of arms into Ethiopia since Addis Ababa switched from the U.S. to the Soviet camp last year.

Hostile neighboring Somalia has charged for months that the Soviets were flying in arms. There was no confirmation, however, until this week when the United States charged that the Soviets started a massive airlift three weeks ago.

The State Department said that in carrying out the airlift the planes were overflying some nations en route from the Soviet Union without seeking permission and in some cases were filing misleading flight plans. Most of the flights are believed to refuel in Aden, South Yemen.

The Nairobi sources said the military buildup has become so urgent and rapid that the Soviets are even flying in ammunition rather than sending it by sea.

Most of the military equipment is being sent to the beleagured Ethiopian forces in the Ogaden desert where Somali troops are reported to have captured 90 per cent of the region.

Government forces, however, still control the region's two major towns, Dire Dawa and Harrar, and are believed by military analysts to be content with holding their current positions until the new Soviet equipment has been absorbed and troops properly trained.

Then they are expected to launch an offensive against the Somalis.

Ethiopian forces have also suffered continuing losses in the 15-year-old guerrilla war in Eritrea where a major battle is under way for Massawa, one of the country's two ports.