State Department spokesman Hodding Carter III forsook foreing policy yesterday to expound on honor and integrity in a commencement address that appeared motivated by the recent resignation of Secretary of State Cyrus Vance.

In what was described as a resignation on principle that was rare in American public life, Vance quit his post April 27, saying he had been unable to support President Carter's decision on the attempt to rescue the hostages in Iran.

In an address at Constitution Hall that he described as "preaching." Carter, who reportedly will also leave the State Department soon, never mentioned Vance by Name. But he said: "There is no cause which can be justified if it does not incorporate individual responsibility and integrity . . . as my former boss just proved."

Carter called for the "ongoing assertion by deed as well as word" of the responsibility of the individual "no matter what the group may believe or decide."

In his 15-minute talk at American University's College of Arts and Sciences exercises, Carter urged adherence to such traditional values as a response to what he saw as doubt and uncertainty now prevailing in the nation.

In a separate address, given at AU's law school commencement, former UN ambassador and undersecretary of State George Bell also described the nation as troubled and torn by doubt. He called on the law graduates "to lead this nation back to the basic faith and values that have been perverted and forgotten by petty and narrow leaders."

While warning against uncritical acceptance of the past or its practices, Ball asserted that the nation should try to "regain a sense of its own 'exceptionalism' . . . that consciousness of a special destiny which ran as a strong and shining thread throughout America's formative years."

In enumerating the values he said the nation once had and now needs, Ball also referred to "that sense of humor we seem to have lost over the past solemn, violent and angry years. . ."

"God speed to you all," he told the graduates."You will not have an easy time of it."

A total of more than 1,600 degrees were awarded yesterday in five separate AU commencements.