The Soviet government tonight "emphatically condemned" Israel's invasion of southern Lebanon and warned that "Israel's aggression against Lebanon and the Palestinian people is once again taking the Middle East to a dangerous line."

"The Soviet Union demands an immediate cessation of Israel's armed invasion of Lebanon and a pullout of the Israeli troops," a government statement said.

Moscow called on the United Nations Security Council to "immediately take measures to curb the aggression and to compel Israel" to respect previous U.N. decisions and the sovereignty and territorial integrity of Lebanon.

Although the statement, distributed by the news agency Tass, warned that "a new military explosion" in the Middle East would "threaten universal peace," it stopped short of making any direct threats. Political observers here said this suggested that Moscow is hoping that the new crisis could be contained quickly.

Meanwhile, Syria, which is Moscow's pivotal ally in the Arab world, has not announced formally whether its forces would come to the aid of the embattled Palestinian guerrillas in southern Lebanon.

Diplomatic sources last week said Syrian President Hafez Assad has been trying to upgrade the Soviet-Syrian friendship and cooperation treaty to include firm Soviet pledges of support in a situation such as the present one.

Tonight's government statement contained only a veiled warning to Israel.

The Soviets bitterly assailed the government of Prime Minister Menachem Begin for allegedly trying by its drive into Lebanon "to drown in blood the Palestine resistance movement and remove altogether from the agenda the question of the exercise of the legitimate rights of the Palestinians."

The statement said the Israeli action "was undoubtedly undertaken with consent and support from Washington."

The statement and a subsequent Tass commentary both asserted that the Israeli push into Lebanon "is a direct consequence of the Camp David deal and American-Israeli strategic cooperation."

The Tass commentary asserted that the United States "bears full responsibility for the present bandit action of its ally" by encouraging Israeli "hawks" to pursue "an increasingly adventurist and bellicose policy" in order to "threaten directly not only the Middle East but also the adjacent regions."

United Press International added the following:

The seven Western leaders at the Versailles economic summit said in a communique that they "were deeply disturbed" by the fighting, which they said could have "disastrous consequences for the whole region."

President Reagan and the leaders of France, Britain, Canada, Japan, Italy and West Germany issued the communique.

Japan said the Israeli invasion "could bring serious results," adding that the attack was "a serious violation of the sovereignty, territorial integrity and political independence of Lebanon."

In Australia, the Sydney Morning Herald said Monday, "The Middle East and its tensions are at its very heart, and this sudden eruption of large-scale conflict on its Lebanon front should compel President Reagan and Mr. Haig to think hard about their priorities.

"The savagery of its Israel's military reaction following the shooting of the Israeli ambassador in London on Thursday cannot be justified, especially as the PLO was quick to deny responsibility."