Egypt's bitter feud with Libya reflects serious Egyptian alarm about Soviet penetration of Africa that is seen by President Anwar Sadat as a threat to his own security, according to authoritative government sources.

Having broken with the Soviets himself, Sadat is now said to be genuinely concerned about what he sees as a major Soviet-Cuban effort to radicalize Africa and isolate moderate and pro-Western leaders such as himself. Sadat sees the leader of Libya, Col. Muammar Qaddafi, as a willing agent of this design.

During his recent rip to the United States, Sadat sought to portray himself as an anti-Communist bulwark in Africa who deserved American aid for his efforts. Egyptian officials familiar with his thinking say this was not just a ploy to obtain U.S. military aid but an expression of concern about events in Libya, Ethiopia, Zaire, Souther Africa and around the Red Sea.

An editorial last week in the newspaper Al Akhbar, a mouthpiece of the government on foreign policy, summed up the Egyptian view.

Commenting on alleged efforts by pro-Soviet Ethiopia and Libya to ovethrow Sadat's ally, President Jaafar 'Nimeri of Sudan, the paper said, "The scheme is being supplied with russian arms stockpiled in Libya and with the Libyan people's oil revenues, and Russian experts from Libya are training the Ethiopians who will carry it out in Ethiopia. The idea is to turn African continent and to enable the Russians to control the Red Sea."

This outlook, informed Egyptians say, explains Sadat's recent involvement in African affairs. This has stirred memories here of comparable maneuvers by his predecessor, Gamal Abdel Nasser, 15 year ago.

Sadat has entered into a defense pact with Sudan and brought that country into the "joint political command" of Egypt and Syria.Egypt has sent a small team of officers on a fact-finding mission to Zaire and announced its support to Morocco's decision to send troops there.

Sadat is participating in an effort by anti-Communist Arab states to entice Somalia out of the Soviet orbit. Egypt is supporting the secessionist rebellion in Ethiopia's Red Sea province of Eritrea. At last month's Afro-Arab summit conference, held in Cairo, the Egyptians pledged $1 million in aid to the black liberation movements of southern Africa. Saudi Arabia, which is working with Egypt and Sudan to counter radical influence in Africa, promised $1 billion in new economic assitance to the Africans.

"What Sadat is trying to do," says an Egyptian policymaker, "is to show the Africans that other paths besides the Soviet one are open to them, that Egypt can help them, too, through its contacts with the Americans and the Arabs."

Sadat, he said, "thinks in Cold War terms. If the Russians aren't with him they must be against him, and he reacts to that feeling."

In a speech to graduating military academy cadets last week, the Egyptian defense minister, Gen. Mohamed Abdel Ghani Gamassi, said that while the primary responsibility of the army is to deal with Israel, "we are not oblivious to the conspiracies taking place for the West" - a reference to Libya - "or to our duties in the south, where Sudan faces a threat."

Egyptian officials and foreign diplomatic analysts, however, say it is highly unlikely that Egypt, which has by far the biggest army in Africa, would become involved militarily in any of these potential conflicts, except possibly in Sudan. Nasser's military intervention, in Yeman and, under United Nations auspices in Katanga in the 1960's; turned out badly for this country, and the Egyptians have long memories.

Egypt is confining itself to political, diplomatic and propaganda efforts, and the immediate and most urgent target in Libya. The Qaddafi government is perceived here at the arsenal and the bank for leftist adventurism throughout Africa.

Libya has made vast purchases of sophisticated Soviet weapons that are said by military experts to be far beyond the absorptive capacity of its own armed forces. Egyptian fears that this equipment was destined for radical states in sub-Saharan Africa were stirred anew, when Cuban President Fidel Castro spent nearly two weeks in Libya at the start of his recent African tour.

The feud between Egypt and Libya, which has flared up periodically for some years, is now intense, with each country accuring the other of sabotage, terrorism and intimidation. Last week Egypt barred Libyan citizens here from leaving the country, in effect holding them hostage for the safety of the estimated quarter million Egyptians living in Libya.

Yesterday, Egypt formally protested to the Arab League about Qaddaffi's actions. Denouncing Qaddafi for plotting against Sudan and for violating the security of Chad by seizing a portion of its territory, the Egyptian note called the Libyan leader "a catt's paw of regimes which are alien to Africa and which are striving to undermine the progress of peoples who aspire to a better future."

Asking that Arab League Secretary General Mahmond Riad circulate this note to all league members, Egypt said that Libya had become a "haven for international criminals" and was bringing brutal repression on its own people.

Foreign Ministery officials said, however, that Egypt had no plans to formally sever displomatic ties with Libya. In theoray, the two countries remain, with Syria, members of "Confederation of Arab Republics," with a common parliament, but this has been a dead letter for years.

Egypt has also refrained from making a formal break with Ethiopia, although relations have deteriorated into open hostility.

Egyptian officials were distressed by public attacks on Egypt by the Ethiopian leader, Mengistu Haile Mariam and a protest march on the Egyptian embassy in Addis Ababa, but there has not been any public protest so far.Scathing denunciations of Mengistu in the Cairo press, however, leave little doubt about what Sadat thinks.