MANILA, Philippines (AP) _ The foreign office is investigating reports that the Soviet Union and Vietnam have offered aid to Communist rebels in the Philippines, the government news agency said today.

The New People's Army, armed wing of the Communist Party of the Philippines, said in a statement that reports of foreign aid offered the rebels were part of the military's ''disinformation campaign.''

Meanwhile, former Defense Secretary Juan Ponce Enrile called for a ''realistic'' attitude toward nuclear weapons possibly stored at U.S. military bases here.

Enrile told the Foreign Correspondents Association of the Philippines: ''If you have a policy written in the constitution that prohibits the entry of nuclear weapons into our territory, what good are these American military facilities?'' He referred to Clark Air Base and Subic Naval Base.

The United States has refused to confirm or deny the presence of nuclear weapons at the bases or on ships that call at Subic.

The constitution, approved last month, says, ''The Philippines, consistent with the national interest, adopts and pursues a policy of freedom from nuclear arms in its territory.''

Enrile, whom Mrs. Aquino fired from her Cabinet after an alleged coup attempt by military officers close to him last November, said the Philippines should outlaw nuclear weapons only when it can afford to defend itself.

Nationalist and leftist groups have called for the dismantling of the bases, saying their presumed nuclear stockpiles expose the country to danger from nuclear accidents or a nuclear attack.

The Philippine News Agency today quoted Foreign Secretary Salvador Laurel as saying he has ordered a probe into a newspaper story saying the Soviet Union and Vietnam ''offered weapons, finance and training'' to the 18-year-old Communist insurgency.

The probe, PNA said, was to be conducted by the European affairs section of the foreign office.

PNA quoted Laurel as saying the March 10 report by the Manila Bulletin, which quoted an ''intelligence document'' was ''cause for deep concern.''

Officials at the Soviet and Vietnamese embassies could not be contacted for comment. Soviet officials have repeatedly denied previously that they were aiding Philippines rebels or had any intention of doing so.

The New People's Army charged in a statement that reports of foreign assistance to the rebels were ''patently fabricated'' by the military and planted in local media ''to diminish the NPA's prestige and credibility.''

In another development, the Roman Catholic hierarchy today told priests and nuns to stay out of politics and movements that espouse class struggle and violence.

Chief of Staff Gen. Fidel V. Ramos told troops Tuesday in Butuan City on northern Mindanao island that the church had been infiltrated by Communists.

Today's admonition was issued by Cardinal Jaime L. Sin, archbishop of Manila, and three capital area bishops during a breakfast forum for reporters.

Bishop Teodoro Bacani said the church must undertake a ''cleansing of ranks'' because politicized priests and nuns ''are undermining the church's credibility.''

On Thursday, the military announced it had captured a priest with a band of New People's Army rebels on Mindanao.

Today, police said weapons charges had been filed against a priest, Rev. Rogelio Arguelles, after troops found a weapon, ammunition and ''subversive literature'' in his rectory on Panay island.