A grenade hurled at the home of black leader Robert Mugabe and a rocket attact against the house of one of his supporters today underscored the increased political violence that has brought Rhodesia's election campaign to a precarious stage only three weeks before the balloting.

The attacks came less than 48 hours after Rhodesia's British governor, Lord Soames, had announced a series of measures to fight voter intimidation. Until today, the British had directed most of their public complaints about intimidation of recalcitrant elements of Mugabe's Zimbabwe African National Liberation Army, who have refused to enter cease-fire assembly points set up by the British under the Dec. 28 truce.

Concerned at the escalating reports of voters intimidation, Soames had already moved on Monday to announce a variety of disincentives.

These included proscribing public meetings of an offending party in certain areas, restricting the time, location and speakers at meetings, prohibiting individual party members guilty of intimidation from campaigning and finally, disqualifying an offending party from contesting the election in a specific area.

The moves were meant to allow Soames to sidestep taking the draconian action of banning a political party from the election entirely, a spokesman explained.

At Mugabe's home, the grenade exploded harmlessly against a security wall, but Magabe associate Kumbirai Kangai was seriously injured when a rocket was fired at his home.

Police have arrested three men in connection with violence, but have not released their names or political affiliation.

At a press conference today, Mugabe blamed the army auxiliaries loyal to the former prime minister, Bishop Abel Muzorewa, for the attacks. He also presented a list of about 40 incidents of alleged intimidation against his party followers around the country, purportedly by the auxiliaries. The black leader said he held Soames responsible for the actions of the forces.

In the past few days, however, the British had been joined in their criticism of Mugabe by both Muzorewa and Mugabe's guerrilla partner, Joshua Nkomo.

Nkomo, coleader with Mugabe of the guerrilla war effort, railed against political intimidation by not only the auxiliaries loyal to Muzorewa but also the Mugabe forces. He claimed one of the parliamentary candidates had been kidnaped by Mugabe's men.

Western diplomats monitoring events here and other independent observers concede that the criticism of Mugabe's troope is, in the main, justified. However, they point out that the British administration, meant to be impartial, is laying itself open to charges of bias by adopting considerably milder public indignation toward allegations of indiscipline and intimidation by the controversial auxiliaries.

The British government takes the position that the auxiliary forces are part of the Rhodesian security forces and therefore owe political allegiance to no single black leader. Nevertheless, the auxiliaries, estimated at 20,000, were originally formed as Muzorewa's private army in mid-1978 and numerous contacts with journalists and other observers have shown that they still retain loyalty to the prelate-politician.

Lord Soames has deployed the auxiliaries in rural black reserves to help reestablish administration knocked out by the guerrilla war that lasted seven years. They are used in civic projects like rebuilding bridges and reopening schools. In addition, they help the white-officered police maintain law and order.

All these activities establish the auxiliaries in the minds of rural peasants as "winners" of the guerrilla war -- a persuasive reason to vote for the bishop, who is favored by the auxiliaries.

Their freedom of movement allows them to drum up support for the bishop, and journalists have heard numerous acounts of how the auxiliaries have ordered reluctant supporters onto the buses at gunpoint to attend one of Muzorewa's rallies.

While Mugabe conceded that his party followers and army were not perfect, he said he resented the "prominence" given to intimidation by his forces and the lack of prominence to wrongdoing by the auxiliaries.

This prominence is largely due to the Rhodesian security forces' continued practice of issuing daily communiques listing breaches of the cease-fire and acts of intimidation by Mugabe's men. Similar lapses by the security forces and auxiliaries do not appear in the communiques. Although he has the power to do so, the governor has not ordered these communiques to cease and as a result only the misbehavior of Mugabe's followers gets publicized daily.

British spokesmen say they have not received specific allegations of auxiliary intimidation on which to take action. They maintain that violence by the Mugabe forces is much worse and more extensive than that of the auxiliaries.

"There is a problem of substantiation," said one British spokesman, and the auxiliaries represent "a relatively minor problem -- they haven't been 'fragging' buses," he added referring to the rocket attack on a transport bus Sunday night that left 16 black travelers dead.

While the British have refrained from blaming Mugabe followers for the attack, they have allowed the Rhodesian Army to send out communiques to that effect.