The new government in Lebanon is busy clearing away the barricades which have for so long divided the city of Beirut between warring factions. The dismantling of the civil wars in Lebanon began in February, when President Reagan withdrew the US Marines and ended direct American intervention. Progress since then has been slow and by short, gradual steps. It has also been steady. One measure of progress was a statement made in Washington on July 25 by the assistant secretary of state for Near Eastern affairs, Richard W. Murphy, to a congressional subcommittee which startled several congressmen present at the hearing.
According to Mr. Murphy the new government of Prime Minister Rashid Karami is achieving considerable successs in reconciling the various warring factions in Lebanon. And, he said, ''We believe that Syria has been one of the helpful players in these recent developments.''
Back in the days of American intervention in Lebanon, Syria was consistently represented in Washington as being the main cause of the trouble. For a time the United States and Syria were on the fringes of war. American guns and bombs fell in areas of Lebanon where Syrian troops were present.
It is impossible to avoid concluding from the record of events in Lebanon dating from the Israeli invasion of 1982 that American intervention in Lebanese affairs has on balance been unsettling while American withdrawal has allowed local forces to restore stability and begin a new and promising chapter in the troubled story of Lebanon.
In this same context it is being pointed out these days that several of the countries of Southeast Asia that were supposed to fall to communism unless the US won in Vietnam have been prospering since the US withdrew from Vietnam.
Thailand, Malaysia, and Singapore are listed these days along with South Korea and Taiwan as leaders among the ''newly developed countries'' whose economic success has become one of the marvels of this generation. The dominoes have prospered, not fallen.
Southeast Asia has been stabilized by the natural conflict of interest between Russia and China. The balance between those powers has allowed the smaller countries that revolve in the economic orbit of the Western democracies to manage their own affairs.
Two examples of the benign aftermath of American withdrawal do not prove that other parts of the world would necessarily benefit in similar manner from American withdrawal. But it does suggest that American intervention is not always as necessary as seems to be the case in the eyes of a worried government in Washington.
The intervention in Vietnam was fueled by the fear that the whole area would go communist. Lyndon Johnson believed fervently that unless he intervened many a domino would fall to the communists. If the purpose of the intervention was to save countries like Singapore and Thailand from communism, then it must follow that America's human losses in Vietnam were unnecessary.
Would a similar American withdrawal from Central America have similar benign consequences? Perhaps not. But it is arguable that Nicaragua has slipped more toward Cuba and Russia because of American intervention than would have been the case had Washington kept its hands off.
We may find out. Congress is increasingly opposed to the present American role in and towards Nicaragua. It may force abandonment of the contras in Nicaragua and withdrawal of US forces from Honduras. If that happens, we will find out just how important American soldiers are to checking the spread of communism in that area.
At the July 25 hearing one congressman wanted to know from Mr. Murphy how Syria could now be called ''a helpful player'' after having so often been described as ''the troublemaker in the region.''
''Times change,'' said Mr. Murphy.
So, too, do perceptions.