WASHINGTON -- President-elect Joe Biden's nominees to lead his national security team promised a turnabout from the Trump administration's approach to national security, saying Tuesday they would keep politics out of intelligence agencies, restore an emphasis on co-operating with allies, and push for a stronger American leadership role in the world.

Antony Blinken, Biden's choice to be secretary of state, pledged to repair damage done to the State Department and America's image abroad over the past four years. He said he planned to restore career officials to prominent positions in the department and strive to promote inclusivity in the ranks for the diplomatic corps.

"American leadership still matters," he said in remarks prepared for his confirmation hearing before the Senate Foreign Relations Committee.

"The reality is that the world doesn't organize itself," he added. "When we're not engaged, when we don't lead, then one of two things happen: either some other country tries to take our place, but probably not in a way that advances our interests or values. Or no one does, and then you get chaos. Either way, that does not serve the American people. Humility and confidence should be the flip sides of America's leadership coin."

President Donald Trump withdrew the United States from a number of international agreements, disparaged NATO allies and questioned the need for multinational approaches to trade, security, economic and environmental issues.

Biden is pushing for quick Senate confirmation of his nominees to lead the departments of State, Defence and Treasury, as well as Homeland Security and the intelligence community. Most are unlikely to be confirmed before Biden takes the oath of office at noon Wednesday, although protracted delays are not expected.

Biden's nominee to lead the intelligence community, Avril Haines, promised to "speak truth to power" and keep politics out of intelligence agencies to ensure their work is trusted. Her remarks implied a departure from the Trump administration's record of pressuring intelligence officials to shape their analysis to the president's liking.

"When it comes to intelligence, there is simply no place for politics -- ever," she told the Senate Intelligence Committee.

Haines, a former CIA deputy director and former deputy national security adviser in the Obama administration, would be the first woman to serve as director of national intelligence, or DNI -- a role created after the Sept. 11, 2001 terrorist attacks.

She was given a mostly positive reception by committee Republicans and Democrats, suggesting likely confirmation by the full Senate. Sen. Mark Rubio of Florida, the committee chairman, seemed to allude to Haines' confirmation as a sure thing, rattling off her eclectic career experiences and hobbies, and then joking, "I'm not sure what you're going to do with the rest of your life and this new position."

In the opening hour of her hearing, questions focused on China as a potential adversary, Iran and prospects for containing its nuclear program, and an issue that has taken on added urgency in the weeks since Haines was nominated, namely, domestic extremist violence. Her answers were received with little sign of opposition from panel members.

Haines said domestic extremism was mainly a matter for the FBI and the Department of Homeland Security, but that the intelligence community, which is comprised of 18 intelligence agencies, including the CIA, has a support role in assessing the threat coming from domestic extremists. She said she expects that intelligence agencies would be involved in those discussions, particularly if there are connections between Americans and foreign-based extremist groups. She said she understand that such connections to international groups do exist, although she mentioned none by name.

In prepared remarks, Blinken said he is ready to confront challenges posed by China, Iran, North Korea and Russia.

Ahead of the Blinken hearing, the top Democrat on the Senate Foreign Relations Committee, Robert Menendez of New Jersey, said he expects the committee to vote on the nomination on Monday.

Blinken promised to bring Congress in as a full foreign policy partner, a subtle jab at the Trump administration and Secretary of State Mike Pompeo, who routinely ignored or bypassed lawmakers in policy-making.

Also testifying Tuesday at his confirmation hearing was Alejandro Mayorkas, Biden's nominee for secretary of the Department of Homeland Security. He would be the first Latino and first immigrant to lead the agency.

Mayorkas faced questions from Sen. Rob Portman, the Ohio Republican who chairs the Homeland Security committee, about an inspector general's report that criticized his management of an investor visa program that he oversaw as head of the immigration services committee under President Barack Obama. The IG said that he created a perception of bias by overturning decisions on behalf of three investment projects backed by prominent Democrats.

Mayorkas strongly defended his actions, saying he intervened in many decisions at the agency on behalf of Republican and Democrats in Congress when he felt that the action was legitimate and necessary to solve problems such as those with the investor program.

"I learned of problems and fixed them," Mayorkas said.

Several senators said it was important to quickly confirm a new head of Homeland Security given the threats facing the nation from the pandemic, the massive SolarWinds cyber-hack that authorities suspect was carried out by Russia, and the rising threat of domestic extremists.

Putting his national security team in place quickly is a high priority for Biden, not only because of his hopes for reversing or modifying Trump administration policy shifts but also because of diplomatic, military and intelligence problems around the world that may create challenges early in his tenure.

The most controversial of the group may be Lloyd Austin, the recently retired Army general whom Biden selected to lead the Pentagon. Austin will need not only a favourable confirmation vote in the Senate but also a waiver by both the House and the Senate because he has been out of uniform only four years.

Also facing confirmation hearings were Biden confidant Antony Blinken to lead the State Department, and Janet Yellen as treasury secretary, another first for a woman.

Austin was testifying later Tuesday before the Senate Armed Services Committee, but the panel will not be in position to vote until he gets the waiver. Republicans are expected to broadly support the Austin nomination, as are Democrats.

Biden's emerging Cabinet marks a return to a more traditional approach to governing, relying on veteran policymakers with deep expertise and strong relationships in Washington and global capitals. Austin is something of an exception in that only twice in history has a recently retired general served as defence secretary -- most recently Mattis. Austin, who would be the first Black secretary of defence, retired from the military as a four-star general in 2016. The law requires a minimum seven-year waiting period.