In a television address last night, President Nixon revealed plans to withdraw 150,000 additional troops from South Vietnam by May 1971-with further withdrawals depending on the progress of the Paris negotiations.

Although the 150,000 figure was triple any previously announced troop cut, a White House official said that the pullout rate would remain the same as in recent months because of the lengthy withdrawal period.

Nixon explained that he was able to set this goal because of the successful pacification program. "The decision I have announced tonight means that we finally have in sight the just peace we areseeking. We can now say with confidence that pacification is succeeding," he said.

"We can say with confidence that the South Vietnamese can develop the capability for their own defense," he continued. "We can say with confidence that all American combat forces can and will be withdrawn."

While promising that "we shall withdraw more than 150,000 over the next year if we make progress on the negotiating front," Nixon said that he "must report with regret that no progress has taken place" in the quest for a negotiated settlement.

Nixon dealt only briefly with the touchy military situation in Laos and Cambodia, merely stating that thousands of Communist troops are on the offensive in those countries in violation of the Geneva agreement.

With the new cutback announcement, the authorized U. S. troop ceiling in South Vietnam by May 1971 will be 284,000 compared with a peak of 549,000 in early 1969.