Four hijackers armed with a pistol and knives seized a Vietnamese airliner today and killed two crewmen before forcing the vintage DC-3 land here where they appealed for political asylum, officials reported.

They said the government, which does not have diplomatic ties with Vietnam, was considering the hijackers' request.

Nguyen Van La, pilot of the comandeered craft, told a news conference that the hijackers took over the plane while it was on a domestic flight from Saigon to Phu Quoc island west of Saigon. He said there were 34 Vietnamese passengers aboard, including the hijackers, and six crew members.

The flight mechanic and radio operator were shot to death by the hijackers, La said, and a steward was knifed and severely wounded.

La said the hijackers may have had some support aboard the plane, a twin-engine, propeller-driven craft. "Some passengers who talked to the hijackers appeared to be in agreement with their actions," he said.

There was no official comment from Saigon or Hanoi but the hijacking was sure to further strain relations between Vietnam and Singapore.

A Singapore government statement said, "An inquiry will be held to determine the facts which will then be processed in accordance with international laws and conventions governing such matters."

Singapore officials said the hijackers, reportedly armed with a pistol and three knives, were being held at the Seletar military air base where the DC-3 landed and that the other passengers and crew were taken into Seletar.

The hijackers had ordered the plane to land at Thailand's Utapao airfield to refuel before flying about 1,000 miles south to Singapore on the southern tip of the Malay peninsula. Thai authorities reportedly refused a request for asylum at Utappao, an air base used by U.S. warplanes during the Vietnam war.

The plane was allowed to land at Seletar when the pilot radioed that he was running out of fuel.

Singapore authorities first removed the wounded steward and the passengers and crew disembarked after the hijackers surrendered.

La told reporters the hijackers took over 15 minutes after the plane left Saigon. "A hijacker held a pistol at my neck while another held at knife at my co-pilot, Mai Ban Bay," La said.

In August 1976, 1 1/2 years after the Communist takeover in Vietnam, a former South Vietnamese soldier tried unsuccessfully to hijack a French plane at Saigon's Tansonnhut Airport. The official Vietnam News Agency said the would-be hijacker killed himself with a grenade, but there were no reported injuries among passengers or crew.

Since the 1975 defeat of the U.S. backed Saigon government, thousands of Vietnamese have fled their homeland, most by boat.

Many of these "boat cases" have had serious problems in finding countries to accept them. Most Southeast Asian nations have all but shut their doors to new refugees.

Even those that do provide haven try to move the refugees on as quickly as possible. Despite these efforts boat camps have sprung up from Thailand to Japan with refugees forced to live aboard the vessels that carried them from Vietnam.