President Nixon will reserve the right to resume bombing North Vietnam if the Hanoi government ignores its "understanding" with Washington on U. S. reconnaissance flights over the North.

Nixon told his first televised press conference since July 30, "if our planes are fired upon, I will not only order that they return the fire" but will order them to respond with full attacks on the military sites involved and their surrounding "complexes."

Nixon also warned that other military sites and supply lines in the North will be attacked if he decides that North Vietnam has stepped up its infiltration of troops into the South and its military buildup along the border beyond the level of the "understanding."

When pressed to reveal in greater detail the progress of his Vietnamization program, the president refused to specify a date for the final withdrawal of American troops. He repeated that he would continue to withhold the information as long as the Paris peace talks continue.

The president also said that Ambassador David Bruce's recent criticism of the communist negotiators in Paris does not mean that the U. S. is abandoning hopes for the peace talks. Nixon added his own criticism of the Hanoi government, branding it an "international outlaw."

Confirming a statement made earlier in the day by Secretary of State Rogers, Nixon said that he will not send ground troops into Cambodia in the future. But he strongly urged Congress to approve his $225 million aid program for Cambodia, calling it "the best investment in foreign assistance that the United States has made in my political lifetime."

The president refused to comment on the Scranton Commission's report on campus violence. Nixon said that the text of a letter he has sent to Scranton will be released within the next few days.