Black nationalist guerrillas shelled Rhodesia's main international airport last night but apparently failed to damage its buildings or runway.

In a terse communique, the Rhodesian military command said "a number of mortar bombs" were fired "in the vicinity of Salisbury Airport." Authorities said 15 rounds of mortar that had been aimed at the airport but that all had failed to fall even inside the perimeter.

It was the first time the guerrillas have attempted such an attack on the main airport, only nine miles from the center of Salisbury. The airport also is used by the military.

The action can only add to the uncertainty already surrounding civil aviation here following the downing of a second Air Rhodesia Viscount airliner last Monday, outside Kariba on the Zambian border, killing all 59 persons aboard.

In Lusaka, Zambia, Joshua Nkomo, leader of the Zimbabwe African People's Union, said his guerrilla forces were responsible for the mortar attack and alleged that buildings, the runway and some aircraft had been hit.

Reporters who inspected the airport this morning, however, could find no evidence of any damage. Workmen were putting tape and sheeting on the windows of the main terminal to prevent them from shattering in case of another attack. Helicopters were seen hovering above the airport every time a plane landed or took off.

The guerrillas that mortared the airport -- just one hour before an Air Rhodesia plane from Johannesburg arrived -- escaped into the night before the military could mount a search.

Meanwhile, a white pilot and his three black passengers were all killed when their light aircraft hit a landmine on a dirt strip north of Mrewa, 45 miles northeast of here. It was the first time guerrillas have planted mines on an airstrip.

The spate of air incidents in the past 10 days has raised serious questions about the future of civilian aviation in this country. Already, Air Rhodesia pilots have issued a statement saying they can no longer guarantee the safety of passengers flying on internal routes. South Africa Airways has suspended stops in Salisbury by its Boeing 747 flights en route to and from European capitals.

In another development, the Rhodesian Parliament approved a new constitution today, 48-6. The dissenters were all black members.

The new constitution provides for black majority rule after the elections scheduled for April 20 but also guarantees extensive white influence in the new government.