A Spanish-born Roman Catholic priest has been found bludgeoned to death, the 11th missionary to die in the past three months in remote areas of Rhodesia where black guerrillas are fighting the white minority government.

A church spokesman said the Rev. Jose Manuel Rubio Diaz, 58, who had lived in Rhodesia for 28 years, was apparently killed by guerrillas. His body was found yesterday, battered and mutilated, about 80 miles from the Mozambique border in southeastern Rhodesia.

On Feb. 6 seven white Roman Catholic priests and nuns were slain at the Musami mission 36 miles northeast of Salisbury.

Here in the capital, Prime Minister Ian Smith was presented with one of the worst political crisis in his career - a revolt within the ruling Rhodesian Front Party over Smith's plan to let blacks buy land previously reserved for whites and drink in white bars.

A dozen members of the party in the 66-seat House of Assembly said they will vote against the proposal, charging that it would leave the government no bargaining power in talks with black nationalists over the majority rule issue. Smith has argued that the plan will weaken the cause of the black insurgents.

Since 13 of the 16 blacks in the House have said they would abstain, the defection by the whites left the proposal with little chance of getting the two-thirds vote needed to pass.

Since Smith came to power in 1963, two years before Rhodesia's unilateral declaration of independence from Britain, his government has passed every piece of legislation it introduced in Parliament.

[In Johannesburg, South Africa police sources said they had arrested Douglas Sherck, an American mercenary who allegedly deserted from the Rhodesian army with two other Americans last month. Sherck is being held on charges of illegal entry and unlawful possession of guns, sources said.]