Bolton commended the work of various UN humanitarian agencies, its assistance in preparing elections in transitional states and in certain peacekeeping roles.
But he said the United Nations is clearly in need of reform. He cited problems with the UN Human Rights Commission and General Assembly, saying the political will of member states was a problem. Bolton also said the scandal over the UN's administration of the oil-for-food program in Iraq revealed deep bureaucratic flaws.
"The potential of the United Nations is often sadly diluted by the encrustations of bureaucracy that have grown up over the years and it's very important that in order to be able to justify the large amounts that administrations every year request for Congress to appropriate, that we can make the case that we are acting to make the United Nations a more efficient and uncorrupt organization," Bolton said.
Bolton's nomination has provoked strong opposition from some former U.S. diplomats and Democratic Party lawmakers. But supporters in Washington say he is well suited to lead a reform effort that top UN officials have also said is badly needed.
Bolton sought to clarify his stance on the United Nations, saying his consistent position has been to make the United Nations more effective. His sharpest criticisms, he said, came in response to UN policies espoused by the administration of President Bill Clinton.
"[The] consistent theme of my writings is that for the UN to be effective it requires American leadership," Bolton said. "I say it over and over again. I deeply believe it. My criticisms during the 1990s were in large measure because of what I thought was the lack of effective American leadership."
The top Democrat on the Senate Foreign Relations Committee, Joseph Biden, raised doubts about Bolton's critical statements about the UN and international laws. And like other Democrats, Biden said Bolton appeared to lack faith in negotiations to head off threats on nuclear proliferation matters, thereby undercutting U.S. interests.
"Foreign policy is not a popularity contest," Biden said. "We must confront hard issues. Sometimes they require hard choices that other countries don't like. But above all, they require American leadership. That's the kind that persuades others to follow. And I'm not convinced this nominee has that as his strongest suit."
Bolton served during Bush's first term as under-secretary of state for arms control.
Committee member John Kerry, who challenged George W. Bush for the U.S. presidency last year, praised the proliferation security initiative that Bolton has championed. But said his overall record on proliferation issues was lacking.
"On two of the most critical proliferation issues facing us, both North Korea and Iran, Secretary Bolton opposed the idea of direct negotiations with each of these countries even when our allies were asking us to do so," Kerry said. "And that's an important part of the diplomatic effort that we're going to have to engage in going forward."
Republicans also had questions about Bolton's plans for UN reform but were more supportive. They control the Foreign Relations Committee by 10 votes to eight for the Democrats. A vote on Bolton's nomination is expected on 14 April and, if approved, it would come before the entire Senate, which is controlled by Republicans.