Moscow — When Soviet military advisers showed up recently with Syrian forces based inside Lebanon, reports from the area say, it was almost as if the Kremlin men actually wantedm to be spotted.
''We called in the Soviet ambassador in Beirut for an explanation,'' a senior Lebanese source told a Monitor Mideast correspondent. ''He denied they were there. But we knew the restaurant where the Russians were eating at the time.''
Visibility - physical, military, and political - seems to be the watchword for Moscow's Mideast planners these days.
In the case of Lebanon - where Secretary of State George Shultz is hoping to rescue US efforts at a negotiated foreign troop withdrawal -the aim seems to be to remind the parties at the bargaining table that other important voices remain to be heard from.
In other words, even should Mr. Shultz manage to wrap up an accord largely on neighboring Syria and, at least indirectly, on the Syrians' arms patrons in the Kremlin.
Generally, while continuing to be leery of a too-confining commitment to Israel's Arab foes, the new Kremlin leadership has been moving to:
* Publicly stress ties with Syria, the closest thing Moscow has to a reliable ally among Israel's key Arab adversaries. Signal No. 1: the installation earlier this year of updated Soviet antiaircraft missiles there, manned by Soviet personnel.
* Parallel to this, ward off any Israeli military tangle with the still outgunned Syrians.
* Dissuade other Arab leaders, specifically Palestine Liberation Organization chief Yasser Arafat and Jordan's King Hussein, from a go-it-alone venture into a US-sponsored negotiating process with Israel.
* Reply to a generally heightened US Mideast profile since the Lebanon war by demonstrating a more active relationship with various other Mideast actors. For example: The Soviet Navy commander, Adm. Sergei Gorshkov, recently visited Saudi Arabia's strategically placed Marxist neighbor, South Yemen. And when radical and unpredictable Libya sent its No. 2 leader here recently, the Soviets declared ''in principle'' agreement to seal a formal friendship pact with the Libyans.
* Reciprocate any moves by important, pro-Western Arab states - that is, Egypt and Syria - toward normalized ties with Moscow.
With the possible exception of the moves in Syria, none of this yet means a major shift in Kremlin strategy, much less in the balance of power in the Middle East.
Moscow still is largely reacting to US moves - recently, to US setbacks - in this area, or to Arab moves.
In general Moscow continues to tread with care. The Kremlin declared accord ''in principle'' on a friendship pact with Libya - but not yet a pact itself. Even with Syria, escalated Soviet backing has so far stopped well short of public saber rattling.
Syria is the main focus of Soviet attention.
Moscow knows Syrian leader Hafez Assad is a past master at balancing superpower ties. His isolation in the Arab world has nudged him closer and closer to Moscow, but most diplomats here say he's still nothing like a mere Soviet surrogate.
Yet political pressures have given Damascus and Moscow key shared interests - to curb US-supplied Israel and discourage moderate Arabs from playing footsie with the Reagan peace plan. They have also hiked Mr. Assad's military dependence on the Kremlin.
Pravda's proclaimed assumption is that Mr. Reagan no longer has a serious chance of enticing either Jordan and or the PLO into his negotiating process.
That leaves a more immediate issue: If Mr. Shultz gets Lebanese and Israeli accord on a troop withdrawal from Lebanon, will Damascus deliver the Syrian pullout essential to activating it?
The public word so far from Damascus has been: ''No, unless the Israelis pull out totally, without the outposts Israel would like to retain in south Lebanon.''
The Soviets have publicly said the same and suggest in dealings with foreign diplomats the fervent hope that Mr. Assad doesn't change his mind.