President Robert Mugabe of Zimbabwe yesterday defended his controversial decision to grant asylum to fleeing Ethiopian president Mengistu Haile Mariam in May as helping to facilitate settlement of Ethiopia's civil war.

"I don't see any basis for criticizing Zimbabwe for having given him refuge. What is a country like Zimbabwe expected to do . . . to shoot him down as he came?" Mugabe asked reporters during a brief news conference at Blair House at the end of a two-day visit here.

He made clear, however, that Zimbabwe had not been involved in any prior negotiations over Mengistu's fate. In fact, Mugabe said, "I did not know that Mengistu was coming to Zimbabwe to seek asylum until he had taken off from Nairobi and was in the air" bound for Zimbabwe.

Mengistu fled Ethiopia May 21 after a 17-year rule marked by continuing civil war and periodic famines. His surprise departure came as rebel forces closed in on the capital, Addis Ababa, a few days before the United States convened an Ethiopian peace conference in London. At the urging of a top State Department official at the talks, rebel forces entered the capital May 28 to restore order.

Officials of the Eritrean People's Liberation Front, one of the former rebel groups, have called for Mengistu's return to Ethiopia to be tried as a war criminal.

Mugabe said the United States did not object to his decision to grant Mengistu asylum because "they couldn't resist, of course," removing him from Ethiopia. "The United States, I understand, also had advised that he should leave the country," Mugabe said.

Mengistu "hasn't yet told us what his future plans are. But we have accepted him on humanitarian grounds," Mugabe said. "And in fact, there was agreement between him and others that his departure would facilitate discussions between the then-government, his own regime, and other groups. . . . Really, his departure was meant to facilitate a settlement between the opposing groups in Ethiopia."

Mengistu is believed to be living on a farm he had purchased previously in Norton, about 30 miles southwest of Harare, the Zimbabwean capital. Mugabe reportedly owns a farm nearby.