Career Diplomat Richard B. Parker arrived today to become the first permanent U.S. ambassador to Lebanon since terrorists killed Francis E. Mely last June.

Commenting that in 19 months of civil strife "Lebanon had descended into chaos and come back," Parker said. "Now is the time for reconciliation and reconstruction."

Parker, 53, last served in Beirut as a political officer from 1961 to 1964 and until recently was U.S. ambassador to Algeria.

In Jerusalem, meanwhile, Prime Minister Yitzhak Rabin told the Israeli Cabinet that Syrian troops have begun pulling back from positions near Israel's border with Lebanon, but the redeployment will not be completed until after the U.S. Secretary of State Cyrus R. Vance arrives in the Mideast.

"The continuation of the handling of this subject will take place during the Secretary of State's visit," beginning Tuesday, a Cabinet communique said.

It said Defense Minister Shimon Peres reported the Syrian withdrawal from the Lebanese town of Nabatiyah, eight miles north of Isreal, is easing tensions on the border.

In other Middle East developments:

A group of Palestinians accused of plotting to kill Vance during his coming Mideast tour were arrested Wednesday by Palestine Liberation Organization security forces, Palestinian sources said in Cairo.

The suspects belonged to the "Black June" organization that came to the fore following clashes in Lebanon between leftist Palestinian forces and Syrian troops, the newspaper Al Qatab reported in Kuwait.

Austrain Chancellor Bruno Kreisky said in Vienna he has received a document from the Palestine Liberation Orgainzation that represents a total change in PLO policy regarding a Middle East peace settlement, The document, published by the Arbeiter Zeitung newspaper, said that a Palestinian ministate could live in peace with Israel.

In Geneva, U.N. Secretary General Kurt Waldheim said his recent tour of Egypt, Syria, Saudi Arabia. Jordan and Israel clarified the positions of all parties in the Mideast. Waldheim said he believes the Geneva conference can be resumed, but if this is not possible, "We have to look out for other means" to achieve a peace settlement.

Saudi Arabia's decision to raise the price of its oil by only 5 per cent this year reflected its desire that the United States and other nations apply presure upon Israel in favor of the Arab cause, Foreign Minister Prince Saud Faisal said in an interview with a Saudi newspaper.