Vietnam is prepared to keep its occupation troops in Cambodia "until hell freezes over" and will escalate its presence there in response to any outside military pressures, Australian Foreign Minister Bill Hayden said today.

He said these points were made by Vietnamese Foreign Minister Nguyen Co Thach during talks in Hanoi last week. Hayden visited Vietnam June 29 to July 1 to see if Australia's new Labor government could help promote a solution to the conflict over Cambodia, which Vietnam invaded in December 1978.

Hayden concluded that Australia does have a role to play in line with his government's desire to take a more active interest in Southeast Asian affairs. But he made clear at a news conference here that this latest venture into the Cambodian fray by a foreign intermediary had produced no progress.

The stalemate, despite a recent flurry of diplomatic activity, illustrates not only the intractability of the Cambodian problem but an apparently hardening attitude by Vietnam's main adversaries -- the noncommunist states of the region and China.

According to Hayden, the Chinese recently set out a "harder" position on the Cambodian problem in a communication with the Australian government. He declined to elaborate.

Western diplomatic sources also said they believe that the members of the noncommunist Association of Southeast Asian Nations -- Thailand, Indonesia, Malaysia, the Phillipines and Singapore -- are less willing to compromise on the issue now than they were during the first three years of the occupation, when the Vietnamese presence in Cambodia appeared more threatening to them.

ASPEAN has led a campaign for support of a U.N. resolution calling for withdrawal of Vietnamese forces from Cambodia followed by free U.N.-supervised elections. China has added an insistence that Vietnam announce a timetable for its withdrawal as a condition for beginning talks with Hanoi on normalizing relations.

In his talks in the Vietnamese capital, Hayden said Thach "sought to portray a great deal of flexibility" on Cambodia.

Hayden said Thach rejected Thailand's recent demand for a 30-kilometer (18-mile) Vietnamese pullback from the Thai-Cambodian border before the Thai foreign minister would accept an invitation to visit Hanoi. Thach told Hayden that Vietnam was willing to discuss the proposal, but Thai Foreign Minister Siddhi Savetsila has said he would only visit Hanoi to talk about Cambodia as a whole, not to negotiate the pullback.

Despite the Vietnamese attempt to display flexibility, Hayden said Thach stood firm on maintaining forces in Cambodia until the perceived threat from China and the Peking-backed Khmer Rouge guerrillas dissipates.

"Vietnam will stay in Cambodia until hell freezes over if that's necessary," Hayden said. He said Thach made it clear that "military pressures will not succeed" in driving out the Vietnamese, and that if these pressures escalate, Vietnam will increase its presence in Cambodia. Hayden expressed fears that such a development could lead to increased Vietnamese dependence on the Soviet Union and a greater Soviet presence in Vietnam.

Hayden said Thach denied that Hanoi intended to "Vietnamize" Cambodia by sending in hundreds of thousands of civilian settlers. He said Thach insisted that the number of settlers would be limited and indicated that no more would live in Cambodia than before 1970, when the figure is believed to have been 500,000.