Fifty black civilians have been killed and 24 wounded in what is the worst recorded loss of civilian life in a clash between Rhodesia's government troops and black nationalist guerrillas in this country's six-year-old war.

The shoot-out comes less than two weeks after Rhodesia's newly formed biracial interim government launched an effort to wind down the war by offering amnesty to guerrillas who laid down their arms.

Instead, the war, which ties down an estimated 65,000 black and white government soldiers, has worsened. Last week, guerrillas burst into the dining room of a luxurious mountain hotel, raining the guests with machine gun fire and killing two white women.

The latest deaths occured Sunday night when a routine bush patrol by security forces came across a group of querrillas holding a political meeting with African tribesmen in a curfew area, according to a statement from Rhodesia's combined military operations headquaters here.

The government troops opened fire on the guerrillas, killing the one addressing the civilians. "This resulted in other groups of terrorists opening fire from different positions at security forces, across and through the tribesmen," the statement said. "In the resulting firefight 50 curfew-breakers were killed and another 24 wounded."

Practically all of Rhodesia's more than 1,500 miles border is under a dawn-to-dusk curfew after which government forces have orders to shoot on sight anything which is moving. In some rural areas, where guerrilla activity is intense, the curfew also extends into several hours of the day.

The communique did not state where the battle took place but one unconfirmed report placed it in Gutu, an area reserved for blacks about 120 miles south of this capital city. The military report also did not identify the guerrillas, but it is known that the Zimbabwe African National Liberation Army (ZANLA), headed by Robert Mugabe, operates in this region.

Prime Minister Ian Smith said in an interview Monday that the ceasefire effort has taken longer than expected to "get off the ground." Both guerrilla leaders, Joshua Nkomo and Robert Mugabe, who together form the Soviet-dacked Patriotic Front, have rejected the amenesty offer and vowed to continue fighting.

A cease-fire between the government and the estimated 7,000 guerrillas now operating inside Rhodesia is crucial for the black-white transitional government set up under the Salisbury agreement signed by Smith and three moderate black leaders March 3.

Without an end to the fighting which ranges over two-thirds of this southern African country, elections for a black majority government cannot be held. According to the Salisbury accord, the former British colony run by whites for 90 years will attain black majority rule Dec. 31 of this year.

Two of the moderate leaders in the interim government, Bishop Abel Muzorewa and Rev. Ndabaningi Sithole, have claimed that the guerrillas support them and will stop fighting once they are convinced they will not be harmed if they surrender.

Because the latest incident was provoked by government troops, it may lead to recriminations against the white-led army by Muzorewa and Sithole, who have not been able to convince significant numbers of guerrillas to stop their fighting.

A large sector of black opinion, while supporting the biracial government, opposes the way the amnesty offer was made because it requires the guerrillas to surrender their weapons to government forces, therefore implying defeat.

Rodesia's 260,000 whites are watching the new government's cease-fire campaign apprehensively. For many of them, its success or failure will determine whether or not they remain in Rhodesia.

Yesterday's communique also reported 37 other deaths in the last three days. It said that 12 black civilians were killed by guerrilla forces; 8 gurrillas and 13 "collaborators" were shot by government troops; two black government soldiers were killed and two civilians died when their vehicle struck a land mine.

The six-year-old war has resulted in more than 9,000 reported deaths to date.