Americans overwhelmingly view Islamic State terrorists as a serious threat to vital U.S. interests and, in a significant shift, widely support airstrikes in Iraq and Syria, according to a new Washington Post-ABC News poll.

The nation’s increasingly hawkish mood will form part of the backdrop for a speech by President Obama on Wednesday, when he will outline his thinking on how to confront the threat from the Islamic State. Obama’s remarks will come a day after he confers with congressional leaders at the White House about the administration’s planning.

Obama’s speech also comes at a critical moment in his presidency. He will address the nation at a time of record or ­near-record lows in public assessments of his performance. Only 43 percent of Americans say he is a strong leader, the lowest reading since he entered the White House. Just over half the country says his presidency has been a failure, although partisanship colors that judgment.

His overall foreign policy ratings are his lowest yet in a Post-ABC News poll. A majority says the president is too cautious when it comes to international problems and specifically in dealing with Islamic State militants. His handling of Russian aggression in Ukraine receives somewhat better marks, but more than 4 in 10 still say he is too cautious.

Over the past month, Obama has authorized limited military airstrikes in Iraq against the Islamic State and sent several hundred U.S. troops to the region to protect American personnel.

View Graphic Public strongly backs airstrikes against Islamic State; Obama struggles politically

But he has faced increasing calls from lawmakers in both parties to expand the U.S. military role, not only in Iraq but also in Syria, where the administration has been reluctant to intervene directly in that country’s civil war.

The speech and session with congressional leaders are aimed at generating strong public backing and support from Congress for whatever mission Obama decides to launch. Congressional leaders said late Monday that they do not expect the White House to ask for authorization for his new strategy, according to senior House and Senate aides.

White House press secretary Josh Earnest, at his Monday briefing, stopped short of saying the president would ask for congressional authorization but made it clear that the administration is seeking to have lawmakers bear joint responsibility for the policy going forward.

Obama, in an interview Sunday on NBC’s “Meet the Press,” said the goal will be “to degrade and defeat” the Islamic State with the help of a global coalition. But he has said he will not put U.S. ground forces into Syria. On Monday, two Republican senators, Johnny Isakson (Ga.) and Lindsey O. Graham (S.C.), urged Obama to include the use of U.S. Special Operations forces as part of an air-ground operation.

“There is a role for Congress to play here,” Earnest said, adding the administration would work to ensure lawmakers “feel like the partners that they actually are, as the elected representatives of the American people.”

Support for military action has risen dramatically in just the past few weeks, coinciding with the beheadings of two American journalists, James Foley and Steven Sotloff, which were recorded on video and released to the world by Islamic State terrorists.

Today, 71 percent of all Americans say they support airstrikes in Iraq — up from 54 percent three weeks ago and from 45 percent in June. Among those who say Obama has been too cautious, 82 percent support the strikes; among those who think his handling of international affairs has been about right, 66 percent support them.

Nearly as many Americans — 65 percent — say they support the potentially more controversial action of launching airstrikes in Syria, which Obama has not done. That is more than double the level of support a year ago for launching airstrikes to punish the Syrian regime for using chemical weapons.

Support for arming Kurdish forces opposing the Sunni insurgents in Iraq also has risen over the past month, from 45 percent in August to 58 percent in the new survey.

Republicans are most supportive of military action, but sizable majorities of Democrats and independents also support airstrikes in both Syria and Iraq.

Public support for action in Iraq and Syria stands in sharp contrast to overall war-weariness seen in earlier surveys after a decade of conflict in Iraq and Afghanistan. The support appears to reflect perceptions of the threat posed by the Islamic State insurgency. Nine in 10 Americans now see the militants as a serious threat to vital U.S. interests, and roughly 6 in 10 say they are a very serious threat.

As support for military action in Iraq and Syria has risen, public assessments of Obama on foreign policy have declined. Just 38 percent approve of his handling of international affairs, and 56 percent disapprove, with 43 percent strongly disapproving. Through most of the spring and summer, his foreign policy approval rating has hovered in the mid-40s.

Obama has been criticized over the past month as appearing disengaged or reticent in the face of a series of international crises. Two moments in particular provoked negative comment. One came when he said that “we don’t have a strategy yet” for dealing with Islamic State militants. The other came when he denounced the beheading of James Foley and promptly went out for a round of golf on Martha’s Vineyard during his vacation.

The president’s overall approval rating is 42 percent, near a low for his presidency. Disapproval stands at 51 percent, not quite as high as it was during the worst of the controversy over the botched rollout of HealthCare.gov in the fall of 2013.

His approval rating on the economy is also 42 percent and has not improved through the course of the year despite evidence of an economic recovery. About 7 in 10 still rate the state of the economy negatively. A majority of Americans say the economy has begun to recover in their own lives, but even in this upbeat group more than 6 in 10 say it has been a weak turnaround.

On health care, 38 percent approve of the president’s performance, showing no improvement as the Affordable Care Act has increasingly taken hold. Roughly 4 in 10 say the law should be repealed, while another 4 in 10 support it. An additional 15 percent do not support the law but nonetheless say that it would be best now to let it go and see whether it works.

Obama’s best numbers in the poll are split verdicts. About half of respondents say that he is honest and trustworthy and that he understands the problems people in the country are having; an almost identical number say he is not honest or empathetic.

The president’s standing is of vital importance to Democratic candidates in November, particularly those in competitive Senate races. There long has been a sharp partisan split in public assessments of Obama, but he has suffered from overall deterioration on some measures.

More than half of all Americans say Obama has done more to divide the country than unite it (55 percent to 38 percent). In May 2013, the last time the question was asked, there was an almost even split. Today, slightly more than a quarter of Democrats share this assessment, along with roughly 6 in 10 independents and almost 9 in 10 Republicans.

At the same time, judgments of congressional Republicans are even harsher, with 27 percent saying they have done more to unite than divide the country and 63 percent saying they have done more to divide it. One-third of Republicans say those in their congressional wing have been dividers.

Immigration is another weak spot in assessments of Obama. Just 31 percent approve of his handling of immigration issues, a drop of seven points since June as the influx of undocumented children on the border created a new problem for the administration. Since the beginning of 2013, when he began to push Congress to enact comprehensive immigration reform, his approval rating on the issue has fallen 18 points.

Despite those low ratings, a slight majority (52 percent) of Americans say Obama should use executive action to deal with the immigration issue if Congress fails to act. White House officials announced Saturday he would delay any such action until after the November elections, after protests from Senate Democrats that such a move could hurt their chances in the midterm elections.

Among the immigration elements under consideration by the administration is action to prevent possibly millions of those here illegally from being deported. The new poll found that 46 percent say those undocumented immigrants should be given the right to live and work here legally, with 50 percent opposed.

As a voting issue, the scales tilt slightly against a candidate who supports such a path to citizenship. Thirty-six percent say support for legalization would make them less likely to vote for such a candidate, compared with 27 percent who say it would make them more likely.

The new survey portrays a country still in a sour mood heading toward the November midterm elections. Nearly two-thirds say the country is seriously off-track. A quarter say they have positive feelings about the way the federal government works, and of the roughly three-quarters with negative views, 49 percent are dissatisfied and 25 percent say they are angry.

Just 15 percent approve of the way Congress is doing its job. One-third say they approve of the way congressional Democrats are handling things, while 21 percent approve of how congressional Republicans are managing. Fewer than half approve of their own representative.

Asked whether they lean toward voting for the Democratic or Republican candidate for House in their district, 46 percent of registered voters say Democrat and 44 percent say Republican. Among likely voters, it is 47 percent Republican, 44 percent Democrat. In both cases, based on past history, the numbers are clearly favorable for Republicans.

The Post-ABC poll was conducted Thursday through Sunday among a random national sample of 1,001 adults reached on conventional and cellular phones. The margin of sampling error for overall results is plus or minus 3.5 percentage points.

David Nakamura, Scott Clement, Robert Costa, Juliet Eilperin and Ed O’Keefe contributed to this report