Moscow — As Ronald Reagan tries to jawbone the US Senate into OK'ing the sale of AWACS radar planes to Saudi Arabia, a Saudi neighbor and sometime friend is holding summit talks with the Soviet Union.
The neighbor in question is not South Yemen, already squarely in the Soviet camp, but North Yemen, which has been trying to chart a policy course between the two superpowers while getting arms from both of them.
Initial indications Oct. 27 were that the North Yemenis were not contemplating a sudden departure from their brand of ''positive neutrality and nonalignment,'' reaffirmed at a Kremlin dinner with Soviet leaders.
Arab and Western diplomats here say North Yemeni President Ali Abdullah Saleh has probably come to Moscow, on the eve of the Senate AWACS vote, to:
* Court Kremlin goodwill at a time of increased strain with the Saudis, and military pressure from South Yemeni-backed rebels at home.
* Seek to reschedule debts for past purchases of Soviet weaponry and perhaps contract for further arms. (Senior Soviet military figures joined President Leonid Brezhnev in an airport welcome for Mr. Saleh Oct. 26.)
* Discuss joint development projects with the Soviet Union for his desperately poor, but strategically important, state.
The very fact of the North Yemeni's visit, which diplomats say was originally scheduled for earlier in the year but was pushed back by the Yemeni leader, is seen as a victory for the Soviets in the sharpened superpower rivalry over the Mideast.
The Soviets are seen as hopeful of using the visit by Mr. Saleh to improve their own ties with him, while encouraging his regime toward at least gradual entente with Marxist South Yemen.
In what may have been part of a bid by Mr. Brezhnev to allay North Yemeni fears over the pro-Soviet South Yemeni regime, the Soviet leader was quoted as telling Mr. Saleh Oct. 27 that ''the Soviet Union never had nor now has any evil schemes with regard to the states of the Mideast. . . . It does not seek military bases on the territory of Arab countries.''
If Mr. Saleh does ultimately move closer to the South Yemenis, this would serve to lessen their isolation in the region at a time when another, more moderate, Gulf state, Kuwait, is trying to encourage its neighbors to open relations with Moscow as well as Washington. Kuwait, alone among moderate Gulf oil states, has formal diplomatic ties with the Soviets.
Kuwaiti Minister of State for Cabinet Affairs Abdulaziz Hussein is now in the Soviet Union. He is the second senior Kuwaiti official to visit here this year.
Another traditionally moderate Arab state to the north of Kuwait, Jordan, also held recent summit talks here. As King Hussein prepared for coming talks in the United States, a generally reliable Arab diplomatic source here Oct. 27 confirmed press reports that Jordan had sealed a weapons deal with Moscow, although describing the accord as ''not big.''
None of this suggests that the Arab world is suddenly, irrepressibly swinging toward the Kremlin. But diplomats say the Kremlin is having some success in countering US moves to piece together an anti-Soviet coalition in the Mideast.
North Yemen is an important prize in this tug of war. Though so far virtually oilless, it lies beside pro-Soviet South Yemen on Saudi Arabia's underbelly.
North Yemen has the rare distinction of having both Soviet and US military instructors on its soil.