WASHINGTON (AP) _ President Bush called government ''an opportunity for public service, not private gain'' Thursday as he urged senior federal executives to uphold high ethical standards.

''Our principles are clear - that government service is a noble calling and a public trust,'' Bush told 3,700 members of the Senior Executive Service. ''This administration is dedicated to ethics in government and the need for honorable men and women to serve in positions of trust.''

Bush chose his first speech outside the White House as president to re- emphasize a theme he has been sounding all week.

The president, speaking at Constitution Hall, an auditorium owned by the Daughters of the American Revolution, also pledged to make federal jobs ''more challenging, more satisfying and more fulfilling.''

Although most of Bush's Cabinet was present, as were many other top-level political appointees, the bulk of the audience was comprised of career civil servants.

Bush said, ''We're all wise in the ways of Washington, especially you who have served this country with such distinction.''

''We know there are ups and downs,'' he said. But he added, ''I must say, there is a nice feeling around today in the country. I think people, when a new president comes in, do root for him regardless of partisan politics.''

Bush's voice was noticeably raspy as he spoke. Press Secretary Marlin Fitzwater said the president had a head cold.

As he has before, Bush offered straightforward advice for avoiding conflicts of interest: ''simply to know right from wrong.''

''Our duty is to serve, and my strong conviction is that we must do it only for the right reasons. ... Government should be an opportunity for public service, not private gain.''

Bush gave similar talks earlier this week in separate meetings with his Cabinet and with his White House staff. And, on Wednesday, he appointed an eight-member commission to recommend by March 9 a new code of ethics for government officials.