WASHINGTON (Reuters) - US President Barack Obama wants Congress to inject money into a counterterrorism fund to train and equip partners in other countries to fight extremists, an initiative that would be a core component of his plan to address Islamic State in Iraq and Syria (ISIS) fighters, the White House said on Monday.

Obama believes he currently has the authority he needs to address the threat Islamic State poses to American citizens, White House spokesman Josh Earnest said.

But if Obama decided to expand the scope of military operations in Iraq and Syria, he would make a determination at that point on whether he would need additional congressional authorization, Earnest said.

Obama administration officials will hold briefings this week for all members of the U.S. Congress as the president makes his case for an offensive against ISIS militants, congressional aides said on Monday.

Administration officials will hold a briefing for all 435 members of the U.S. House of Representatives on Thursday, a House aide said. Senate aides said there would be a similar session for all 100 members of the Senate as early as Wednesday. President Barack

Obama will deliver a speech to Americans on Wednesday laying out his "game plan" to halt the Islamist group, which has seized swathes of Syria and Iraq, while trying to head off public concerns that the country could be moving toward about another full-scale war.

Obama is meeting with the four leaders of Congress - Senate Majority Leader Harry Reid, Senate Minority Leader Mitch McConnell, Speaker of the House John Boehner and House Minority Leader Nancy Pelosi - on Tuesday, before his speech.