New signs that the influence of the Soviet Union in the Arab world is dwindling and that Soviet policies in East Africa are alienating some of Moscow's longtime allies emerged today from a four-nation summit conference in North Yemen.

Arab and Western diplomatic analysts in several capitals say the conference showed that Semalie, once regarded as virtually a Soviet client state, is moving toward a more independent policy and that South Yemen, a Marxist state with close ties to Moscow is coming increasingly under the influence of moderate and pro-Western Arab leaders.

The conference was held in Taiz, North Yemen, and its issues affect a dozen countries in northern and eastern Africa and the Arabian peninsula, as well as the Soviet Union and the United States.

The participants in the Taiz meeting were the heads of state of North Yemen, South Yemen, Somalia and Sudan. All are members of the Arab League, although most Somalis are not Arabs.

All have coastlines on the Red Sea or its approaches. All, for various reasons, are hostile to their coastal neighbor, non-Arab Ethiopia, and are unhappy with the Soviet Union for its support of the leftist military regime in Addis Ababa.

Although the four leaders issued only a brief, mildly worded communique and named only Israel as a foe, the mere fact that the conference was held amid the current feverish atmosphere in the Horn of Africa and the Arab world is being widely interpreted as heralding major developments.

In essence, the Soviets appear to be losing a diplomatic and ideological struggle with Arab moderates for influence over South Yemen and Somalia, two strategically situated countries where the Soviets have been entrenched for years.

Reports from Taiz say that Jaafar Nimeri, the president of the Sudan - who was once pro-Soviet himself but is now strongly anti-Moscow after several Communist-inspired attempts to overthrow him - succeeded in persuading Marxist South Yemen to accept a reconciliation with its neighbor to the east, the sultinate of Oman. South Yemen has for years supported a leftist guerrilla insurgency against Oman.

If true, the reconcilation would signal a major step by the South Yemen government.

If the reports are true, the reconciliation would signal a major step by the South Yemen government, which has the East German and Cuban advisers, away from the radical camp and toward the bloc of Arab moderates. This would continue a process that began a year ago when South Yemen first established diplomatic relations with Saudi Arabia.

Authoritative Somali, sources say that the decision by Somali President Mohammed Said Barre to participate in the Taiz meeting is a relection of deep Somali unhappiness over Soviet support for the regime in Ethiopia.

In the Somali view, the Soviet cannot be friends with Somalia and Ethiopia at the same time because the two are implacable enemies and the Somalis accuse Ethiopia of usurping vast stretches of territory that should be Somalia's.

Therefore, the Somalis say, Said Barre is willing to listen both to the moderate Arabs, such as Nimeri, and to the United States about possible new relationships. Said Barre publically said as much two years ago, but little had happened to change his country's firm alliance with Moscow until the Soviet Union - aided by Libya and Cuba - stepped in to support the Addis Ababa regime.

The ostensible subject of the Taiz meeting was Red Sea security, which was also a principal topic of a summit conference of Sudan, Egypt and Syria last month.

[Nimeri stressed the economic co-operation aspects of the conference, noting that the participants are among the world's 25 least-developed nations, Agence France-Presse reported from Khartoum, Sudan.]

The Taiz conferees agreed to seek a meeting of all Arab states with Red Sea coastlines to study this issue further. They called for Arab solidarity against "the aggressive policies of Israel and the support Israel receives from Zionist forces."

Israel and Ethiopia are the only non-Arab countries with any shoreline on the Red Seas or its branches. Somali and North Yemeni officials have accused the Ethiopians of allowing Israel to establish a military presence on islands in the Red Sea off the Ethiopian coast. Israel's presumed interest is not only to protect its own shipping lanes but also to help the Ethiopians suppress the Arab-supported secessionist rebellion in the coastal province of Eritrea.

Diplomatic specialists here say, however, that evidence is very scanty of any Israeli military presence in the area.

The real target of Arab concern is Ethiopia, according to Arab and Western diplomats, and by association, the Soviet Union and its friends in Cuba and Libya, who are also supporting the Ethiopian government.

Informed sources here, including Somalis, give this analysis of the complex Ethipia situation, as viewed by the Arabs:

The Sudanese are hostile to Ethiopia because Ethopiopia is friendly with the Soviet Union and Libya, which Sudan accuses of having jointly sponsored a coup plot last summer. Sudan is openly supporting the Eritrean rebels.

Egypt, which is allied with Sudan, and Saudi Arabia, which is using its money and influence to counter radical Influence throughout the Middle East, are anxious about the possibility that the Soviet Union will gain a dominant position in Ethiopia. Both Yemens are concerned about the purported Israeli role in Ethiopia and are also supporters of the Eritrean movement.

The Somalis have extensive territorial claims against Ethiopia and are hostile to anyone supporting the Ethiopnians against them.

This, according to Somali officials, is why the Somalis, after years of near-total dependence on Moscow and uneasy relations with their anti-Communist partners in the Arab League, may be on the point of changing direction.

It was apprehension about this posible change in Somali allegiance that led Cuban President Fidel Castro to make an unannounced visit to Somalia during his current African tour, which began in Libya and included Ethiopia, according to diplomatic analysts.

After meeting Castro, however, Said Barre held three days of talks with Nimeri in SOimalia, and it is taken for granted that Nimeri, who is anti-Moscow, anti-Libya and anti-Cuba, gave Said Barre the other side of the story.

Niemri is understood to have the support of Egypt and Saudi Arabia in what appears to be an effort to woe the Somalia and South Yemenis away from the pro-Soviet camp. The Saudis were recently reported to have offered $300 million in military and other aid to bring Said Barre along.