The number of whites leaving Rhodesia rose sharply last month to 1,342 - the most for any month since last December.

Figures released yesterday by the Central Statistical Office showed that only 231 immigrants arrived in July, so that the net loss was 1,111. This was the biggest drop in the dwindling white population now totalling about 230,000, since May 1977.

The surge in the white exodus is widely attributed to a loss of confidence in the ability of Rhodesia's biracial transitional government to end the country's six-year-old guerrilla war.

Meanwhile, government leaders, including Prime Minister Ian Smith, planned meetings with former U.S. Treasury secretary John Connally, who arrived from South Africa yesterday for a two-day visit. Connally and his wife were met at the Salisbury airport by Picter K. van der Byl. white cominister of foreign affairs and were to be guests at the ranch of Andre Holland a white member of parliament.

In Geneva, a United Nations panel made public the names of 1,439 corporations, banks, organizations and individuals it accused of giving political, economic or military aid to white minority governments in southern Africa. The list covered links with Rhodesia in violation of U.N. sanctions.

In another development, police reported that the government's "most wanted" black nationalist guerrilla, whom they did not identity, was killed near Salisbury Monday night during gun battles in which a white policeman and two black civilians also died.

The guerrilla had been the object of a manhunt since last week's fighting between security forces and guerrillas in Highfield Township, about eight miles from the white center of Salisbury.

Police said he was the last survivor of a squad of assassins sent into the country by Joshua Nkomo, coleader of the Patriotic Front nationalist guerrillas, to kill leading black members of the government.