WASHINGTON — President Obama plans to address the nation Wednesday to outline a broader offensive against Sunni militants in the Middle East, a move welcomed by a number of key congressional leaders who have come to view the extremist group Islamic State as an increasingly menacing threat to the U.S.

Foreshadowing his remarks in an interview aired Sunday on NBC’s “Meet the Press,” Obama said that it was time for the U.S. to “start going on some offense” to beat back Islamic State fighters.

“I’m preparing the country to make sure that we deal with a threat,” Obama told NBC.

Meanwhile, the U.S. military made clear the expanding scope of its air campaign against the extremist group, with American fighter and bomber jets conducting a new series of strikes near the Haditha Dam in western Iraq. The dam is controlled by Iraqi security forces, but has been under frequent attack by Islamic State fighters intent on seizing it, the Pentagon said.

As the Obama administration seeks to put together a coalition to act against the Islamic State, the secretary-general of the Arab League provided encouragement Sunday.

Nabil Elaraby told member foreign ministers gathered in Cairo that Arab states must unite to confront the threat posed by the radical group, also known as ISIS, which has seized large chunks of territory in Syria and Iraq, killed thousands of adherents to non-Sunni religious faiths, threatened Iraq’s government and the semi-autonomous Kurdish region and beheaded two American journalists.

Western action against the Islamic State would be greatly eased by an Arab call for joint action, Elaraby told the ministers, citing previous accords under which member states would defend one another.

Since Aug. 8, the U.S. has conducted 143 airstrikes on Islamic State targets in Iraq, actions Obama has said have been designed to protect people against genocidal attacks and to safeguard key property including the huge Mosul dam on the Tigris River.

The airstrikes near the Haditha Dam, which took place late Saturday and Sunday, were meant to protect the Euphrates River facility, which provides fresh water for millions of Iraqis as well as crops.

“The potential loss of control of the dam or a catastrophic failure of the dam – and the flooding that might result – would have threatened U.S. personnel and facilities in and around Baghdad, as well as thousands of Iraqi citizens,” Pentagon Press Secretary Rear Adm. John Kirby said in a statement.

Despite his actions thus far, Obama has been criticized by some for failing to set a clear strategy on how to deal with the Islamic State, reflecting his reluctance to commit American forces to another war in Iraq. In the wake of the militants’ attack on minority Yazidis in Iraq and the beheadings of the American journalists, there have been growing calls from Congress and others for more aggressive action.

“What I want people to understand is that over the course of months, we are going to be able to not just blunt the momentum” of the militants, Obama said on NBC on Sunday. “We are going to systematically degrade their capabilities. We’re going to shrink the territory that they control. And ultimately, we’re going to defeat them.”

Although Obama said there would be a “military element” to the strategy, he added that “this is not going to be an announcement about U.S. ground troops.”

“This is not the equivalent of the Iraq war,” he said. “What this is, is similar to the kinds of counterterrorism campaigns that we’ve been engaging in consistently over the last five, six, seven years.”

Obama’s planned speech Wednesday suggests that he is preparing a new phase in U.S. military action and would be seeking to rally the American public – and Congress – behind the broader mission.

Among those in Congress welcoming such action was Sen. Dianne Feinstein, D-Calif., who chairs the Senate Intelligence Committee.

“I think that this is a major change in how ISIS is approached,” she said Sunday on CNN’s “State of the Union,” noting the coalition that the U.S. has forged with a number of allies, including some Middle Eastern countries, to counter the militant fighters.

“It is overdue,” she said, “but the president is now there, and I think it’s the right thing for America.”

Feinstein said she supported deploying the American military’s special operations forces and cracking down on sources of Islamic State funding, among other more aggressive actions.

“ISIS is a major threat to this country in the future,” she said, noting that she believed the group was seeking to advance to Baghdad and to attack the U.S. Embassy there.

Senate Minority Leader Mitch McConnell, R-Ky., said in a statement that the Islamic State threat was “real and it’s growing.” He urged Obama to “exercise some leadership” and to engage Congress with “a strategic plan.”

Whether Congress will actually vote on Obama’s plan is uncertain. Congressional leaders have said they want Congress to be consulted, but they have not committed to a vote. And though some members of Congress have said they believe that they should go on record concerning military action, others are reluctant to do so with an election coming in less than two months.