Britain's colonial governor of Rhodesia threatened today to defranchise hundreds of thousands of voters in a move that could cost nationalist leader Robert Mugabe the coming general election.

A spokesman for Mugabe declared tonight that "we won't accept a situation where we are disadvantaged" and warned that the colonial administration's move could lead to a resumption of the guerrilla war.

The governor, Lord Soames, issued the warnings today following a growing cycle of violence in Rhodesia in which a number of attacks on candidates and party workers have been attributed to Mugabe's followers. In the past week, however, Mugabe himself has been the target of a least two attacks in which he narrowly escaped serious injury or death.

Lord Soames and Mugabe also escalated their war of nerves in a contentious, 90-minute meeting in which there were exchanges that left no doubt about their serious differences just 15 days before elections to produce a black-majority government.

The governor's spokesman said Soames would issue an ordinance Wednesday proclaiming his authority to call off the elections and prevent people voting in any district where he determined that intimidation had made free and fair elections impossible.

Soames, who has absolute powers during the transition period established under a peace settlement reached in London two months ago, has repeatedly complained of wide-spread cease-fibe violations and intimidation by Mugabe's supporters.

The spokesman pointedly added that unless there is "marked improvement" in particular areas, Soames "is determined to use this power . . . to roll back intimidation" in the election campaign.

Soames, the spokesman said, would "look carefully" at intimidation in several areas over the next 10 to 12 days before taking any action.

The spokesman listed 21 elections districts in five of the eight provinces where he said there is particular concern. He acknowledged that the areas were mainly Mugabe strongholds.

Any such move by Soames could cost Mugabe numerous seats. The leader of the Zimbabwe African National Union is generally expected to win the most seats but far from a majority. Disenfranchisement of voters in Mugabe's areas of support could swing the election to one of his rivals, Patriotic Front leader Joshua Nkomo or, less likely, to former prime minister Abel Muzorewa.

Soames' announcement has brought new tension here, however.

Mugabe has threatened in the past to remove his troops from assembly camps and resume the guerrilla war if Soames bans his party from any electoral district.

A Mugabe spokesman tonight indicated that any disenfranchisement would, in Mugabe's view amount to the same thing as banning the party in those areas.

The British spokesman said Soames was trying to take "every step short of banning" Mugabe's party but was "not prepared to organize elections in areas where they could be manifestly unfair." He said Soames might take other actions under the emergency powers he assumed last week allowing him to ban candidates or parties.

The British move could put Mugabe in a difficult position even though Soames would not be acting directly against Mugabe by barring his party.

Delaying action for 10 to 12 days would put the possible disenfranchisement of voters virtually on the eve of the Feb. 27 to 29 elections, leaving Mugabe in the position of pulling out at the last minute.

His 17,000 troops now gathered in assembly camps under the London agreement, would be at a considerable disadvantage because by then the combined 30,000-member Rhodesian military and police would be bolstered by an expected callup of about 70,000 to 80,000 reservists.

Politically, disenfranchisement could have wide-spread effects. Any such move would not reduce the number of parliamentary seats to be chosen by the voters in the 56 election districts but only reduce the number casting ballots.

Reducing the Mugabe vote would give other candidates a larger percentage. The five provinces in eastern, southern and central Rhodesia are all areas where the majority Shona tribe dominates. Mugabe and Muzorewa are both Shonas and are expected to win most of the seats in these areas, particularly in the east.

Muzorewa would undoubtedly lose some votes as well in any disenfranchisement in such areas, but Nkomo, from the minority Ndebele tribe, would probably benefit.

Nkomo's Patriotic Front, technically still loosely aligned with Mugabe, apparently grasped the significance of the move immediately.

Josiah Chinamano, Nkomo's deputy, said that it would be "unfortunate" if such powers were used, but he added that there were areas where some parties could not campaign because of intimidation and he hoped that if Soames acted it would be in those areas.

Muzorewa and Nkomo have complained about being unable to campaign in Mugabe strongholds.

At the 90-minute meeting between Soames and Mugabe, the governor spoke "firmly" to the nationalist leader and "outlined measures he might be forced to take," Soames' spokesman said.

"The governor left Mugabe in no doubt that he took a serious view of the situation in certain areas of the country," the spokesman added.

Mugabe presented Soames with a sharply worded seven-page protest about moves in some areas by the colonial government and inaction in others.

Mugabe complained that numerous protests he had submitted over the last three weeks had received no response. He contrasted this with "over-enthusiasm by you to handle and believe those cases alleged against our forces and supporters by other parties."

He demanded that the security forces "be forthwith confined to their barracks" and said his party "reserves its right not only to defend its members with vigor but also to retaliate with equal ruthlessness."

Complaining that Soames had "destroyed" the truce by imposing "a unilateral cease-fire" on his forces, Mugabe said Soames was now proceeding "to destroy the election process" in order to favor Muzorewa.

Martin Meredith of the Sunday Times of London reported from Salisbury:

Although Mugabe agreed to instruct his guerrillas outside of the camps to surrender, some of his supporters recently captured by security officials have said that more experienced guerrillas were told to hide their arms and stay in villages to ensure voting for Mugabe. They said the guerrillas would form groups of two or three and would intimidate villagers with death threats to gain support for Mugabe. They also said the orders came from Rex Nhongo, a key Mugabe aide in Salisbury.

Soames and Mugabe's opponents are afraid that a fair election cannot be held with the terrorism, according to British sources. Muzorewa and Nkomo have privately complained to Soames that Mugabe's forces are keeping them from drawing crowds in eastern Rhodesia, in the regions of Manicaland and eastern Mashonaland.