President Nixon last night charged before Congress and a nationwide television audience that Hanoi has broadened the Vietnam war into an Indochina conflict. He predicted increased U.S. aid and air support to the South Vietnamese.

In his second annual "State of the World" message, keyed to a "quest for global peace." Nixon pledged to continue U.S. troop withdrawal from Southeast Asia. However, he added that American troops will remain in South Vietnam as long as North Vietnam holds American prisoners of war.

Nixon gave a pessimistic report about the prospects for a negotiated settlement. He said that possibilities for a peace settlement have been prevented by North Vietnamese demands which amount to a "guaranteed political takeover" of the South.

"We will not give up on negotiations," he said, "though the past year has indicated that it will be extremely difficult to overcome the enemy's doctrine, calculations, and suspicion."

Nixon rendered the Soviet Union a veiled threat not to try to dominate the Mideast. He said that the U.S. does not seek a dominant position in thatarea, and added, "We cannot allow others to establish one."

Nixon said that the U.S. is prepared to establish a dialogue with Communist China, but "will not accept the Peking regime's desire to exercise hegemony over Asia."

Nixon appealed for trust in his leadership as he seeks to develop what he called a new, more restrained world role for the U.S. He added that while "cutting back its overseas forces prudently," the U.S. will still live up to its treaty commitments.

At the Paris peace talks Xuan Thuy, chief North Vietnamese negotiator, denied Nixon's charge that his country has widened the conflict. He said that despite the invasions of Cambodia and Laos, Nixon "nonetheless pretends that it is the Vietnamese people... who have extended the war to all of Indochina." Nixon, he added, is "preparing senseless military adventures" against North Vietnam.

The Soviet reaction to Nixon's speech, reported by Tass, said that the U.S. 'remains on its old position of imposing imperialistic terms on the people of Vietnam" at the Paris peace talks.

Nixon's speech, the dispatch added, indicates that further U.S. policy in Laos and Cambodia will continue on the "established course... aimed at suppressing by force of arms the national liberation movement in Southeast Asia."