KHARTOUM, Sudan (AP) _ In a second peace overture since seizing power last week, the military junta led by Lt. Gen. Omar Hassan Ahmed el-Bashir has decreed a one-month unilateral cease-fire in the war with southern rebels.

The junta Tuesday night proposed a general amnesty for all Sudanese who have taken up arms against the government since May 1983, when the rebellion led by turncoat army Col. John Garang began in three southern provinces.

The proposed amnesty in effect would cover the 50,000-60,000 rebels of Garang's Sudan People's Liberation Army.

The junta's actions stretched the cessation of hostilities in the southern regions of Upper Nile, Bahr el-Ghazal and Equatoria into a third month.

Both sides stilled their guns in May and June in response to a unilateral cease-fire proposed by Garang to allow the United Nations to move 120,000 tons of relief supplies to the south to ward off famine this summer.

The new unilateral cease-fire, which took effect Tuesday, and the proposed amnesty were announced in separate statements from the Command Council of the National Salvation Revolution.

The 15-member council overthrew the civilian government of Prime Minister Sadek el-Mahdi Friday in an apparently bloodless coup.

The council said el-Mahdi's failure to end the civil war was among principal reasons for the coup. It pledged to make peace in the south its top priority, saying it would scrap all efforts begun by el-Mahdi and make a fresh start.

El-Bashir's subsequent actions appeared to bear this out. In a Saudi newspaper interview published Monday, said he had invited rebel leader Garang to come to Khartoum for peace talks.

''Inviting Garang to Khartoum is an initiative meant to demonstrate good intent,'' el-Bashir, 45, told the newspaper Okaz.

Tuesday night's announcement ordered ''a one-month truce in all war zones and fighting scenes'' beginning immediately.

Despite el-Bashir's repeated peace vows, spokesmen for the Sudan People's Liberation Army have refrained from comment, saying it was closely watching developments in Khartoum.

The armed forces' official newspaper reported today that el-Bashir told the Ethiopian ambassador that he wanted to send a delegation to Addis Ababa, Ethiopia's capital, to meet with Garang's representatives.

Al-Guwat Al-Musalaha said the rebel command replied Tuesday night that they were ready to talk with representatives of the junta. The newspaper said no date was set for the delegation to go.

The rebels have their political headquarters in Addis Ababa; Ethiopia has backed the rebels with money, arms and training facilities since they began their armed insurrection demanding greater autonomy and a better economic deal for southerners.

After lengthy hesitation, el-Mahdi's government, which took office in 1986, opened peace talks with the rebels in Addis Ababa in May. A new round was to have begun Tuesday, also in the Ethiopian capital.

It junta said it expected the general amnesty would be enacted soon. This should not take long because el-Bashir's council has dissolved parliament.

Besides chairing the council, el-Bashir made himself premier, defense minister and military commander-in-chief. He has promised to form a Cabinet of civilians under the junta's tutelage.

The junta also announced Tuesday that 15 southern politicians who worked for el-Mahdi's government were arrested on charges of corruption.

This brought to 45 the number of political figures the military said they have arrested since the coup. The detainees include leaders of political parties, which have since been disbanded, but not el-Mahdi.

The Cairo newspaper Al-Ahram quoted el-Bashir as saying in an interview that the prime minister, who led the Umma Party, remains at large.

He said el-Mahdi had attended the wedding of a relative in a Khartoum suburb Thursday night and was not at home when troops arrived after midnight to detain him.

El-Bashir also told Al-Ahram he used just 300 soldiers and 10 tanks to seize power. He said the guard force at general headquarters and many other military units immediately pledged loyalty to his movement and that most political party militias had surrendered to the army.