WASHINGTON (AP) _ Secretary of State Warren Christopher, brushing aside suggestions that he envisions a reduced U.S. international role, pledged today that the United States will continue to ''shoulder the responsibility of world leadership.''

''America must lead,'' Christopher said in a speech to a gathering at the University of Minnesota. ''The need for American leadership is undiminished.'' A text of the speech was made available at the State Department in Washington.

Christopher's remarks appeared aimed at neutralizing comments on Tuesday by a senior State Department official who told reporters that the need of the United States to focus on economic problems will require a diminished role internationally.

Christopher disputed the suggestion that the United States can no longer continue its leadership position because of economic problems.

''It's true that the United States faces many challenges today unlike any in the nation's history,'' he said. ''But to me, that means we must be more engaged internationally, not less; more ardent in our promotion of democracy, not less; more inspired in our leadership, not less.''

He added: ''We stand prepared to act decisively to protect our interests wherever and whenever necessary. When it is necessary, we will act unilaterally to protect our interests. Where collective responses are more appropriate, we will lead in mobilizing such responses. But make no mistake. We will lead.''

The State Department aide who generated the controversy over the U.S. role in the post-Cold War era spoke frankly at a reporters' luncheon with the understanding that he would not be identified. He had sketched U.S. foreign policy as calling at times for sharing power with allies, particularly when U.S. security was not at risk.

The official was Peter Tarnoff, undersecretary of state for political affairs, whose name surfaced today in numerous press accounts.

Meanwhile, the Center for Security Policy, in a critical analysis, called the presentation ''the Tarnoff Doctrine'' and said ''the surest way to fritter away power and lose influence in the international arena is to try to husband it.''

After the breakup of the Soviet Union, both the Bush and Clinton administrations indicated the United States would not be ''the world's policeman'' and intervene in every conflict.

The ongoing war in the Balkans and the cautious U.S. response contributed to the current controversy over policy, however.

Critics have questioned whether a package of proposals for Bosnia announced last Saturday would deter the Serbs from taking territory in or protect civilians forced from their homes.

President Clinton had decided the United States and its allies should threaten the Serbs with bombardment of their artillery and with lifting of the U.N. arms embargo against Bosnia. But the allies and Russia disagreed and the plan was shelved after Christopher conferred with them in Europe.

The Christopher aide, speaking anonymously, said that by seeking a consensus with Britain, France, Russia and others on Bosnia the Clinton administration was practicing ''a form of leadership that's quite appropriate at this moment.''

''For those who would like to have (Bosnia) become a U.S. show there is distinct disappointment out there,'' he said. ''But we feel differently about it.''

With the Cold War over, the official went on, there are ''fewer heavyweight bad guys but more midweight bad guys who in many ways are more dangerous.''

But, he said, ''We simply don't have the leverage. We don't have the influence. We don't have the inclination to use military force. We certainly don't have the money to bring to bear the kind of pressure which will produce positive results anytime soon.''

The statements drew a bristling reaction from the White House.

''This official clearly does not speak for the administration on the U.S. role in the post-Cold War world,'' spokeswoman Dee Dee Myers said.

''I'd have to refer you to the State Department for Brand X's future,'' she said.

The State Department spokesman, Richard Boucher, said Christopher had talked to the official, had ''full confidence'' in him and would not discipline him.

On Capitol Hill, during a Senate hearing on foreign aid, Sen. Mitch McConnell, R-Ky., said he was shocked by the suggestion the United States would have a diminishing role abroad.

He said it followed weeks of ''contradictions and confusion'' from Haiti to Bosnia.

''From my perspective, the administration is in serious trouble on the foreign policy front,'' McConnell said. ''American credibility is on the line and no one seems to care.''