Secretary of State Alexander M. Haig Jr. said yesterday he is "appalled" that French banks have agreed to lend the Soviet Union money for a natural gas pipeline, and he said the United States will undertake talks with its European allies this week on cutting off future economic credits.

A State Department official said a delegation led by Undersecretary of State James L. Buckley will visit Europe in an attempt to develop a common allied position on possible new sanctions, in light of a devisive debate that has developed after meetings of NATO's North Atlantic Council.

The dispute is over the meaning of the council's agreement that one ally would not impose sanctions that would undermine the position of the other allies.

Haig, in an appearance on "This Week With David Brinkley" (ABC, WJLA), said that unilateral action by the United States would be "self-defeating," and he condemned the recent unilateral decision by French banks to lend the Soviets $100 million toward the construction of a pipeline from Siberia to Western Europe.

"It's not a step which we favor or condone and which we are quite appalled by," the secretary said.

"If one wants to be effective in the sanction area against the Soviet Union today," Haig said, "the area of greatest payoffs is in future credits, beyond the shadow of a doubt."

He said he discussed future credits with western foreign ministers while he was at the European Security Conference last week in Madrid, and said the ministers agreed that credit was the subject most likely to get allied agreement.

Haig said Buckley's mission to major European allies would deal with the whole question of future western credits to the Soviet Union. A State Department official said the trip would last about a week and talks will be carried on at the level of undersecretary.

Haig also struck on several other topics, including new evidence on Soviet use of chemical warfare and more comments on the recent shipment of Mig jets to Cuba.

He said the United States has new and "incontrovertible evidence" that the Soviet Union is using chemical weapons in Laos, Kampuchea (formerly Cambodia) and Afghanistan, and that these poisons have killed "scores of thousands of non-combatants in all three target areas."

State Department spokesman Dean Fischer said that the new evidence includes more samples of the toxic materials used, as well as a broader variety of evidence than has been presented before on the so-called "yellow rain."

The estimates of casualties from the use of a variety of natural poisons called mycotoxins is the first time the State Department has commented on the magnitude of the deaths.

A Soviet Central Committee spokesman, Stanislav Menshikov, who appeared on the same television program, denied that the Soviets were using chemical weapons and said a United Nations commission that investigated the matter found no evidence of the use of chemical weapons in Asia.

"We are somewhat disappointed" in the U.N. committee's initial conclusion, Haig said, but he said the new evidence has also been turned over to the United Nations for examination. "With every passing day we get more incontrovertible evidence" of the use of mycotoxins by the Soviets and their allies, he said. "There is no question in our minds that such weapons have been and are continuing to be used."

Haig avoided answering the question of whether the Soviet use of chemical weapons has violated treaties against the use of chemical weapons.

On the recent shipments of Mig23 jets to Cuba, he responded with surprise to the comment of Soviet spokesman Menshikov that part of the 1962 U.S.-Soviet agreement that ended the Cuban missile crisis was a U.S. agreement to pull American warplanes out of Turkey.

Menshikov said that the Migs in Cuba are all "defensive" planes and could not be offensive weapons because they have a range of no more than 500 kilometers, so "they could fly to Palm Beach and no farther."

Haig responded by saying that these Migs are "in many ways as capable" as the bombers that the Soviet Union withdrew from Cuba in 1962.

It has been reported in recent weeks that a fresh shipment of a dozen Migs has arrived in Cuba, but it is uncertain whether the Migs are the interceptor type or the type equipped with racks to carry nuclear weapons.