Robert Mugabe and Joshua Nkomo, the joint leaders of the Patriotic Front guerrillas, today postponed their scheduled return to Rhodesia after being advised by the British colonial administration that there was insufficient time to make security arrangements.

Nkomo rescheduled his return for a week from Sunday, but no date has been set for Mugabe's arrival.

Meanwhile, Lord Soames, the British governor, issued a "final" appeal for the estimated 15,000 Patriotic Front guerrillas to report to assembly points by the Friday midnight deadline, as required by the Rhodesian cease-fire agreement signed in London last month.

[Britain released 10 senior guerrilla commanders from Rhodesian jails today, hoping to convince more Patriotic Front fighters to come out of hiding and report to cease-fire assembly points. All of the commanders released were loyal to Mugabe, according to new service reports.]

The postponement of the return of Nkomo and Mugabe, which a Mugabe spokesman here said would set back to peace process, was a sharp reminder of the tenuous control Britain has in its former colony. It is not uncommon to hear members of the 220,000-white minority population, angered over killings in the bloody seven-year war that has enmeshed the country, threaten to kill the two nationalist leaders.

Enos Ncala, a Rhodesian-based official in Mugabe's wing of the Front, said the British "told" his leader not to return Saturday. He added that the move was bound "to have a serious effect on the whole process of peace."

Cephas Msipa, one of Nkomo's lieutenants, said the British action was "an insult," but took it more philosophically.

"One has to face reality. If the poeple who are supposed to safeguard your security say they can't do it, you must take that into consideration," said Msipa.

Nkomo is a prime target of hatred for many whites because troops under his command shot down two Rhodesian civilian airliners.

One veteran African observer of Rhodesia pointed out that Britain needed to have the two guerrilla leaders return to the country as soon as possible. "As long as they are outside the country, they can take actions against the government but it would be harder for them to do so when they are here," he said.

It is believed that their early return could have helped in the process of guerrillas reporting to designated camps, even though they would have arrived after the Friday midnight deadline.

So far only about 5,000 guerrillas have entered the camps, a figure which British sources said was not nearly enough. A British spokesman said the final numbers tomorrow night will be a factor in how Soames continues to govern, implying that it would affect among other things, the question of lifting martial law in most of the country.

British officials are firm in their public statements that the Friday deadline will not be changed, but there are indications that Soames will not take immediate action against those who fail to report. He will be visiting the provincial capital of Bulawayo when the deadline passes.

Nkomo and Mugabe, both of whom spent a decade in prison under the rule of white former prime minister Ian Smith, have been out of the country since 1976 and 1974 respectively.

The British concern about the potential for violence means that rival rallies will not be allowed in major cities at the same time, a spokesman for Nkomo said. This could have an impact on the elections because even if Mugabe and Nkomo return in mid-January, they will only have six weekends in which to campaign.