MOSCOW, JULY 18 -- Two cosmonauts who left the orbiting Soviet space station to repair their damaged Earth-reentry capsule had to use an emergency hatch to reenter the station today after the airlock at the main return port malfunctioned as their oxygen supply was running out.

The incident, which Soviet television reports called "life-threatening," occurred while flight commander Anatoly Solovyev and mission engineer Alexander Balandin were attempting to fix torn thermal insulation on their Soyuz TM-9 spacecraft, which is docked at the Mir space station and which the cosmonauts must use to return to Earth next month.

It was the latest in a series of problems plaguing the cosmonauts' six-month mission, but they joked about it afterward for Soviet television viewers. Solovyev quipped that flight controllers "need to put road signs" on the huge space station.

Radio Moscow said the cosmonauts repaired some of the damaged capsule insulation -- which helps protect the craft from burning up on Earth reentry -- and were nearing the six-hour safety limits on their life-support systems when they returned to Mir and found they were unable to close the outer door to the reentry hatch.

The cosmonauts then had to clamber over the outer surface of the space station to another entry port that leads to a compartment for storing scientific equipment. The government newspaper Izvestia said that at one point the cosmonauts ran so low on air that they had to "feed" their spacesuits with more oxygen, apparently by drawing it from inside Mir.

Soviet space program officials tried to minimize the problem and indicated they expect the cosmonauts to return to Earth as scheduled on Aug. 9. "No one is concerned here. It is an abnormal situation but controllable," a center spokesman said.

But James Oberg, one of the foremost American experts on the Soviet space program, said the loss of critical life-support equipment in the damaged airlock could complicate future space walks and thus make any further needed repairs to the Soyuz capsule problematic. "The general crisis was not fully resolved," Oberg said in a telephone interview.