President Reagan's Senate victory on the sale of AWACS surveillance planes to Saudi Arabia is bad news for the Kremlin. It was also accompanied by two other signs of possible trouble, in the longer run, for Soviet interests in the strategically important Middle East:
* Mr. Reagan gave his first, cautious welcome to a Saudi peace plan for the region, a blueprint envisaging creation of a Palestinian state.
* An Israeli Cabinet minister said the United States had been quietly providing arms to Iraq, a one-time Soviet ally that has turned sour on the Kremlin.
The Soviets' initial public reaction to the AWACS approval was to accuse Washington of scheming to expand its Mideast military presence and to lure the Saudis behind US diplomatic moves in the region. Moscow did not immediately comment on Mr. Reagan's remarks about the Saudi peace plan, nor on the reported US arms to Iraq.
The outcome of the sharpening superpower rivalry over the Mideast will depend largely on the Mideast itself.
Political winds blow there with all the ferocity of the desert gusts the Arabs call the khamseen. Many an Arab regime is rickety. At the top are men with a penchant for playing neighbor against neighbor and superpower against superpower. And beneath this landscape lies a lot of oil.
Neither Washington nor Moscow is likely to exclude the other from the Mideast equation any time soon.
This would seem particularly true as long as a central factor in Mideast conflict - the future of the Palestinians - remains unresolved. This is the stuff of which Arab-Israeli wars are made. If and when there is another one, it seems safe to assume both superpowers will be needed to wind it down.
But in the short run at least, Washington's Mideast fortunes seemed on the rise Oct. 29. This is not the kind of thing Soviet policymakers applaud.
For months, the Soviets have been wooing Arab regimes - and even talking to Israel - in hopes of helping bury once and for all the US-sponsored Camp David negotiating process in the Mideast. As a substitute, they have suggested a widened peace effort giving the Kremlin a participatory role denied it by Camp David. The implication is that the US can ''deliver'' Israel in such a settlement while the Soviets bring in key Arabs, particularly the Palestine Liberation Organization.
US ''imperialism'' and Israeli ''expansionism'' are in cahoots, the argument goes. The only thing Washington can offer the Arabs is humiliation - and surrender. Egypt's separate treaty with Israel, unembellished so far by an agreement on the Palestinians, is cited as an example.
Since even moderate Arabs resent the US-Israeli alliance, the Soviets have managed at least to help complicate, if not bury, US negotiating efforts.
But Ronald Reagan is responding by trying to consolidate his own relations with key Arabs. He is selling AWACS to the Saudis, a move Soviet officials see as a bid to extend US power in the Mideast. And if the Oct. 28 Israeli report on arms deliveries is correct, he is courting Iraq, an oil state that still denies the US an embassy and, on paper though not in practice, is allied to Moscow.
And he has given a welcome - albeit hedged, in presumed deference to the Israelis - to a Saudi peace plan supported by various Arab oil states. PLO leader Yasser Arafat has also welcomed the Saudi proposal, although indicating he won't support it unless other Arabs, including hard-liners, do. This seems unlikely but does suggest that if Mr. Arafat ever goes in on a Mideast peace settlement, he won't necessarily need to be ''delivered'' by the Kremlin.
The assumption among diplomats here is that the US will now try to use the Camp David framework to achieve something approximating, but not including, the Palestinian state sought by Saudi Arabia and other Arabs.
If Mr. Reagan can pull this off, diplomats say, he would deal a further, and severe, blow to Soviet influence in the region.
But the Mideast being the Mideast, his chances are rated as low. Bringing both Israelis and Arabs behind such an arrangement, as one diplomat here put it, ''will be a lot harder than getting the AWACS sale through the Senate.''