Susan Rice: US has ambitious but achievable agenda
Top White House adviser Susan Rice has said the US is pursuing an "ambitious yet achievable agenda" overseas.
Ms Rice argued US leadership had been essential for success on issues like Ebola, Iran's nuclear programme and sanctioning Russia over Ukraine.
President Barack Obama has faced criticism from Republicans in Congress over his foreign policy choices and perceived lack of leadership.
Her comments came as Mr Obama sent his national security strategy to Congress.
The document is a blueprint for foreign policy, defence and national security for the last two years of President Obama's term. It was last updated in 2010.
In a letter outlining the strategy, Mr Obama said the US would "always defend our interests and uphold our commitments to allies and partners".
"But we have to make hard choices among many competing priorities and we must always resist the overreach that comes when we make decisions based upon fear."
Analysis: Tara McKelvey, BBC News
Susan Rice was careful to stick to the script, flowing line by line and turning the pages carefully.
"Yes, there's a lot going on," she says, raising her hands and saying people shouldn't be "buffeted by alarmism".
A moment later she clasps her hands together and describes the "nature of American leadership". It's strong and decisive, she says. Yet for the most part the speech sounds like a list - and her voice has a staccato quality.
She pauses frequently as she ticks off issues, such as cyber security, "economic strength" and "food security".
As a result the overall impression is that she's presenting disjointed talking points, not an overarching strategy, one of the criticisms Republicans have made of Mr Obama's foreign policy.
Among the updates in the policy document was an increased focus on the importance of US oil and natural gas production, combating climate change and promoting gay rights.
The new strategy, and Ms Rice's speech, come as some members of Congress have asked the US to send defensive weapons to Ukraine to fight against Russian-backed rebels.
The White House has said Mr Obama is reconsidering his opposition to the idea but no decisions have been made.
In a speech at the Brookings Institute, Ms Rice, the White House National Security Adviser, said the US was "proudly shouldering the responsibilities of global leadership", including the fight against the Islamic State group.
But she called for "a sense of perspective".
"While the dangers we face may be more numerous and varied," Ms Rice said, they were not "existential threats".
"We cannot afford to be buffeted by alarmism and an instantaneous news cycle."