More than half of the eligible voters among the 230,000 Rhodesian refugees living in neighboring countries will not return home in time to cast ballots in the national election at the end of the month, according to estimates of United Nations officials.

By far, the vast majority of these people are living in Mozambican camps that have given considerable support to Robert Mugabe, a Marxist leader running in the British-run elections.

The loss of this voting support represents another liability for Mugabe, who already faces concerted maneuvering by his political opponents, black and white, to reduce his election chances.

By the time polling begins Feb. 27, about 50,000 refugees are expected to have returned to Rhodesia under the U.N.-sponsored repatriation program, which was part of the London peace agreement signed in December between the biracial government here and the guerrilla Patriotic Front movement of Mugabe and Joshua Nkomo.

All refugees older than 18 among the estimated 63,000 living in Botswana and Zambia would be able to return in time to vote if they wished, according to Nicholas Morris, the Salisbury-based representative of the U.N. High Commissioner for Refugees. However, some of the refugees in these countries, where Nkomo had his camps, are delaying their return until after the election, he said.

Repatriation of the 160,000 Mozambique-based refugees has been slower and a maximum of 20,000 will be back by Feb. 27, Morris said. U.N. officials estimate that 50 percent of the total refugee population is older than 18 thus leaving about 70,000 potential voters in Mozambique. This amounts to about 3 percent of the black Rhodesian voter population.

These people will miss the election for a variety of reasons. Primarily the British made it physically impossible to repatriate all refugees by insisting on a short transition period of two months before the vote. The agreement did not guarantee that all refugees would be brought back for the elections, Morris said.

Secondly, the repatriation program met some initial reluctance from Rhodesian authorities who were "convinced that we are repatriating heavily armed men," Morris said.

The biracial government, as well as the white-officered police and Army, also were no doubt sensitive to the fact that all returning voting-age refugees were potential supporters of the guerrilla leaders.

Their reluctance created a "bottleneck" on the incoming flow of refugees because of the difficulties in finding suitable reception centers and the limited deployment of police officers for the required security checks on the returning refugees, Morris said. But these problems have been sorted out and the security screening is going well, he added.

A far more serious problem, however, is the police detention earlier this month of 70 people returning from Zambia because they admitted to receiving guerrilla training, Morris said. U.S. officials are consulting with British authorities on the issue but not much can be done because the London agreement stipulates that military personnel are not supposed to return until after the election.

Despite local newspaper allegations of torture of those returning refugees, Morris said he was satisfied no one was being mistreated at the centers that are under U.N. supervision.

"But I cannot say what happens to them when they are taken away and moved to the police station," he said.

Last week's detentions highlight the unsettled atmosphere in which the repatriation is taking place. Despite a fairly successful cease-fire, most government and military officials have found it difficult to put the war behind them.

The refugees, meanwhile, are returning when there is no guarantee that the war will not resume and while the parties they have supported in exile are still without power.

"I don't think there's ever been a repatriation quite like this one; it's unique," said Morris. Refugees usually return when there is "no argument about who the government is," much unlike the situation here, he said.

In these circumstances the security screening has aroused hostility and suspicions among returning refugees since it supplies police with names, addresses and, in certain cases, fingerprints, of guerrilla sympathizers that can be referred to if the cease-fire breaks down. Refugees are also asked to fill out a form stating why they left the country.

For many of the refugees, the security check means "they are not quite certain in whose hands they are now," said Judah Gwatiringa, an employe of the Rhodesian social welfare department administering the reception centers under U.N. supervision. "They feel they have been penetrated by the police now that they have been screened."