President Carter expressed skepticism today over the Soviet Union's announced withdrawal of troops from Afghanistan, calling it an "obvious propaganda effort" involving less than 10 percent of the Soviet occupation force there.

In an informal news conference with American reporters at the close of the Venice economic summit meeting, Carter continued the strong anti-Soviet line he has been preaching throughout his visit to Europe.

"It is hard to say what the Soviets will do" ultimately in Afghanistan, he said. "My experience has been not to be optimistic."

The president said the United States believes the withdrawal involves less than 10 percent of the 85,000 Soviet troops thought to be in Afghanistan that none of the withdrawn troops have been involved in combat in recent weeks and that all are positioned for a quick return to Afghanistan.

The question-and-answer session took place in a conference room of the Hotel Cipriani overlooking the waters outside Venice, Carter, dressed in a short-sleeved white sport shirt and blue slacks, appeared unusually relaxed as he sat in an east chair with two bottles of mineral water on a table beside him.

Like the summit conference of the United States and its principal allies that concluded today, the new conference was dominated by questions on international political issues. In response to some of the questions, the president:

Said he was pleased by French President Valery Giscard d'Estaing's recent visit with Soviet leaders and that he looks forward to West German Chancellor Helmut Schmidt's planned talks at the Kremlin later this month. "For the Soviets to hear in unvarnished fashion from European leaders the kind of message [on Afghanistan] they have been hearing from us strengthens our position," he said.

Reiterated the U.S. commitment, agreed to last December by NATO to begin work on the deployment in Western Europe by 1983 of medium-range nuclear missiles capable of reaching the Soviet Union. He said he would be pleased and surprised if the Soviets unilaterally agreed to halt deployment of their own SS20 medium-range missiles, but that such a move should not be followed by a halt in the planned missile deployment by the West.

Strongly reaffirmed his belief that the Middle East peace process begun by the Camp David accords is the "best approach" toward achieving a comprehensive peace agreement. Carter said he made his case to the other leaders and believed he had convinced them. Suggesting his displeasure with the European Common Market's call last week for participation of the Palestine Liberation Organization in the peace talks, Carter said, "We did not encourage that. It could have been worse, but I don't believe it did any harm."

Said he could not discuss reports that Israeli Prime Minister Menachem Begin plans to move his office to East Jerusalem, a step that could call into question the Camp David accords' deliberately ambiguous approach to the final status of the city. But Carter said that the United States opposes "any action of a permanent nature that is incompatible with the Camp David accords," and he added, "I'll let you make the judgement on that."

The president also discussed for the first time his recent letter to Schmidt on the missile issue.

A recent speech by Schmidt suggesting that neither the Soviets nor NATO deploy additional missiles in Europe for the next three years was seen by American officials as a possible step that could unravel NATO's December agreement.

Carter then sent Schmidt a letter restating the U.S. position. Schmidt, in an interview with The Washington Post, called the letter "astonishing" and said he had never softened his own support for the NATO missile deployment in 1983.

Carter said the letter was sent "with the best of intentions" and that in it he had blamed "erroneous press reports" for the confusion over the West German position on the issue.

"I don't think that the letter should have been astonishing, but I'd rather let Chancellor Schmidt tell you about that," he said.

Carter's tone on the announced partial withdrawal of Soviet troops from Afghanistan was markedly more skeptical today than his initial reaction.

He declined to answer a question on whether the United States and its allies might supply direct said to Afghan rebels. He said the joint declaration issued here calling for a complete withdrawal of Soviet troops from Afghanistan was not a sufficient Western response in itself, but when asked if U.S. allies are considering additional steps against the Soviets, he said, "I can't answer that question."

Carter said the withdrawal is "obviously a propaganda effort on the part of the Soviets to repair some of the damage that has been done to their reputation" and to persuade additional athletes to attend the summer Olympics in Moscow.

The president suggested that his personal relations with the other participants here were good. Speaking of his private meeting with Schmidt amid the reports of animosity between them, he said, "Well, it was sweeter and lighter at the end of the conversation than at the beginning."