The Soviet Union, apparently under the pressure of its Middle Eastern treaty obligations, has shifted into diplomatic high gear in an effort to force the Israeli invasion forces out of Lebanon.
But there is no sign the Kremlin is prepared to send troops to the region.
The state-controlled Soviet press made no mention June 10 of a message from President Leonid Brezhnev to President Reagan, who is visiting in Bonn. But Israeli government sources said such a message had been received and that it was ''brutally worded.''
United States and Soviet officials here denied knowledge that such a message had been sent, but it seemed a logical extension of Soviet efforts and comments so far on the Middle East conflict.
''They don't have an awful lot of options,'' said one Western diplomat. ''Their response so far, judging from the press, seems to be directed in a diplomatic direction.''
A diplomatic response realistically seems to be the easiest response the Soviets can make, even though their friends and allies might welcome overt military support. The other, middle, course would be stepped-up Soviet arms supplies to Syria or the Palestine Liberation Organization (PLO).
''It would be awful darn difficult to justify a Soviet troop presence in Lebanon, and secondly to support Soviet troops there. They would be running a very grave risk,'' the diplomat said.
Certainly, the Soviets have made no official response to the call by PLO leader Yasser Arafat for aid. The press has not even mentioned Arafat's plea, although it has given plenty of coverage to the Israeli attacks.
In the absence of action, however, the Kremlin must at least be seen to be exerting pressure on the situation.
The Kremlin is tied into a friendship treaty with Syria, which has troops in embattled Lebanon, and Moscow has long been sympathetic to the PLO (which has a representative and a large house in central Moscow).
But the treaty with Syria calls only for ''consultations'' in the event of military actions by either side. There is no indication the Soviets feel bound to offer any aid to Lebanon, especially as they never favored Syria's taking on a military burden in Lebanon in the first place.
The treaty ''binds the Soviets in no sense of the word,'' said one analyst.
Hence the Soviets have limited themselves so far to issuing ringing statements, which they have done aplenty. In the most authoritative statement on the situation so far, the official news agency Tass Sunday roundly condemned Israel for the ''massive aggression'' and ''bandit action'' that is trying to ''drown in blood'' the Palestine resistance.
Tass called for an immediate withdrawal of Israeli troops from southern Lebanon, blamed the United States for arming and backing Tel Aviv, and urged the United Nations immediately to take measures to halt the fighting.
The prime responsibility of all nations desiring peace is to ''prevent a new military explosion (in the Middle East) which threatens universal peace,'' Tass said.
No doubt the Soviets would like to play a role in any peace settlement that is eventually drawn up. Diplomatic overtures can help to win it a place at the negotiating table, while using force would reap no visible benefits.