In a major shift of tactics. China's senior Communist leaders have told a group of visiting U.S. congressmen that they are willing to negotiate directly with their Nationalist Chinese rivals over the future of Taiwan.

The statements made by Vice Chairman Teng Hsiao-Ping, the second ranking member in Peking's hierarchy, and other top officials seem to be the most conciliatory toward Taiwan President Chiang Ching-Kua's Nationalist government in recent years.

They were reported by a U.S. congressional delegation, led by Rep. Lester Wolff (D-N.Y.), which returned here from China yesterday.

Although negotiations between Taiwan and the Peking government remain unlikely, the statements indicate a new Chinese willingness to moderate harsh anti-Chaing public remarks of the past and try to swing American public opinion in Peking's favor.

Wolff said the Chinese reminded the nine visiting congressmen that the Communist Party and the Kuomintang (Nationalist Party) had cooperated twice before, during a campaign to defeat local warlords and unify the country in the 1920s and during the war against Japan in the 1930s and 1940s.

"There has been no official contact with Taiwan, but you cannot rule out a third time," Rep. Eligio de la Garza (D-Tex.) quoted one high Chinese official as saying.

At a press conference here, Wolff emphasized that the Chinese also made a "strong statement" that did not "rule out by any means the use of force in liberating Taiwan." The Peking officials also showed no sign of retreating from their demand that Washington cut off diplomatic relations with Taiwan, end its mutual defense treaty with the Chiang government and withdraw all remaining U.S. military personnel from the offshore Chinese island.

The U.S. Congress and the Carter administration have been reluctant to take such steps in order to bring full diplomatic relations with Peking without some Chinese guarantee that Taiwan will not be taken by force. Peking has shown little interest in making such a promise, but the statements to Wolff's group appear designed to soften the image in American minds of warlike Chinese belligerence toward the Taiwan government.

The conciliatory statements were volunteered by the people we spoke to - at several points in our discussions," said Wolff, chairman of the Asian and Pacific Affiars Subcommittee of the House International Relations Committee.

In the past, American visitors to China who asked about Peking's attitude toward the Kuomintang have usually been lectured on Nationalist crimes and "blood debits," including the many massacres of Communist Party members carried out by Chiang's late father, Generalissimo Chiang Kai-shek. A Peking commentary on Chiang's move from the Taiwan premiership to the presidency in May said "he has continuously intensified his fascist rule and suppressed the people."

But Wolff, who heard similar lectures when he visited China in early 1976, said such rhetoric was largely absent this time. He said he sensed a "new realism in terms of an emerging Chinese emphasis on seeking ways to settle the Taiwan question on a bilateral basis, between the Chinese themselves, in ways that are acceptable to the parties involved."

He said he also found domestic policies more realistic, as the Chinese move away from harsh domestic measures that had been pursued by the "Gang of Four," a Peking clique led by Mao Tse-tung's wife Chiang Ching that was purged in late 1976.

"I think it's safe to say they were harder on the Gang of Four than on the people of Taiwan," said Rep. Charles Rangel (D-N.Y.) of the Chinese officials they spoke to.

Peking's usual attitude toward Taiwan has been a plea for people on the island to admit their mistakes and come over to the mainland side, rather than a suggestion of talks.

In a March 6 speech, Communist Party Chairman Hua Kuo-feng said he hoped "military and administrative personnel of the Kuomintang" would "clearly see the general trend of events and take the road of patriotism and unification of the motherland."

Peking's last apparent public call for negotiations came in February 1973, when former Kuomintang Gen. Fu Tso-yi addressed a meeting in the Chinese capital. "We are all Chinese . . . Let us come together and talk," he said in a speech supposedly aimed at Kuomintang officials who had not yet come over to the Communist side.

An analyst who has followed Chinese statements closely for the last three years said he could not remember any Peking remarks similar to those made to Wolff's group. One member of the group said the Chinese noted that earlier efforts to cooperate with the Kuomintang had not worked well, but also observed that many communist leaders had attended school with Kuomintang officials.

Wolff said Peking officials told the group that further sales of U.S. warplanes to Taiwan would interfere with negotiations over a solution to the Taiwan issue, but the Chinese did not mention sales to Taiwan by other countries.

The Chinese expressed doubt that the Taiwan government would ever go to the Soviet Union for help if the United States severed relations. Washington has approved sale of Israeli-made fighters with U.S.-made components to Taiwan, but Chiang's government has indicated it prefers to buy more effective U.S.-made fighters. Chiang also does not want to hurt his close ties with Saudi Arabia by dealing with Israel.

Tawian officials have indicated they fear a sharp decline in invester confidence in their booming economy if there is the least suggestion of talks with Peking. In an interview published in the June Reader's Digest, Chiang called such negotiations "totally impossible."

"Negotiation with the Communists is tantamount to suicide. What free world country has ever successfully done so?" he said.

Wolff declined to say which Chinese officials had made the suggestion of talks with Taiwan, but Rep. C. Tennyson Guyer (R-Ohio) said the idea had been voiced by Teng, perhaps the most influential Chinese leader in foreign policy as well as other. The delegation also saw Vice Foreign Minister Wang Hai-jung, Vice Foreign Trade Minister Wang Jun-sheng, Foreign Affairs Institue President Hao Teh-ching and Peking University President Chou Pei-yuan.

Others in the delegation were: Reps. J. Herbert Burke (R-Fla.), Billy Lee Evans (D-Ga.), L.H. Fountain (D-N.C.), James R. Mann (D-S.C.) and Larry Winn Jr. (R-Kan.).