BANGKOK, Thailand (AP) _ Ten years after its forces marched into Cambodia's capital of Phnom Penh, Vietnam on Saturday hailed the planned withdrawal of its remaining 50,000 troops.

The Vietnamese Communist Party newspaper Nhan Dan praised the pullout as ''a convincing proof of the steady growth of the People's Republic of Kampuchea,'' or Cambodia.

Cambodia's government was installed Jan. 7, 1979, when Hanoi's troops ousted the communist Khmer Rouge from power.

In a speech Friday marking his government's decade in power, President Heng Samrin of Cambodia announced Vietnam would withdraw all its remaining forces by September if a political settlement to the Cambodian war is reached.

Vietnam has repeatedly pledged to withdraw the troops earlier than its original target date of 1990, but it had not previously set a date.

The Vietnamese newspaper said the decision, made jointly by the two countries, is a ''new testimony to good will and determination to achieve an equitable solution.''

The anniversary celebrations began Friday with speeches by Cambodian and Vietnamese leaders. In Phnom Penh, public buildings had been painted and streets swept clean.

Nguyen van Linh, general secretary of Vietnam's Communist Party, said Friday the total withdrawal ''must be undertaken simultaneously with the cessation of foreign military aid to all Cambodian sides and of the use of foreign territory as sanctuary against the Cambodian people.''

Heng Samrin said his government hopes other countries will keep promises to end aid and sanctuary to the Khmer Rouge and two other non-communist guerrilla groups. Such promises have been made by China, which arms the guerrillas, and by Thailand, which gives them territory for bases.

''These agreements must be carried out under effective international supervision,'' the president said.

Resistance leader Prince Norodom Sihanouk was quoted as saying, however, that Vietnamese pledges of withdrawals are false, that peace talks have failed and that Cambodia's future can be settled only by continued fighting.

Vietnam's announced intention to withdraw its troops has raised fears that the Khmer Rouge, the most powerful of the resistance groups, would seize power again.

Vietnam, which initially had an estimated 200,000 troops in Cambodia, claims to have made annual withdrawals since 1982. It says the largest came in 1988, when all advisers and 50,000 soldiers returned home.