WASHINGTON — Forecasting the changing nature of threats against the U.S. for years to come, President Barack Obama says “America is at a crossroads.” And so, too, is his presidency’s counterterrorism policy, which has long struggled to balance protecting the nation from terror attacks while upholding Americans’ rights.

The Obama administration this week acknowledged that four Americans have been killed — three of whom were not specifically targeted — in secretive overseas drone strikes against al-Qaida extremists since 2009. And in a wide-ranging speech Thursday, Obama warned that Americans must be vigilant against increasing homegrown threats from within, including from fellow citizens like the surviving suspect in last month’s Boston Marathon bombing.

It is an awkward position for the president, a constitutional lawyer, who took office pledging to undo policies that infringed on Americans’ civil liberties and hurt the U.S. image around the world.

Instead, he defended on Thursday his continued and expanded use of the spy drones, which have killed thousands of terror suspects and civilians, in places like Afghanistan, Pakistan, Yemen and Somalia. He hinted in the speech that he would give law enforcement officials new authority to seize suspicious communications within the United States.

And Obama defiantly promised to push forward with his longtime goal of closing the U.S. detention center at Guantanamo Bay, Cuba, where 166 terror suspects are being held — but said it’s largely up to a resistant Congress to get it done.

Obama acknowledged it’s a tough line to walk in striking a balance.

“Now is the time to ask ourselves hard questions — about the nature of today’s threats and how we should confront them,” Obama said at the National Defense University.

“In the years to come, we will have to keep working hard to strike the appropriate balance between our need for security and preserving those freedoms that make us who we are,” he said.

The president outlined a narrower scope of threats against the United States in the years ahead, with the war in Afghanistan winding down and an al-Qaida that has splintered — in part, due to the very attacks he authorized. But as al-Qaida has fragmented, it has given rise to smaller networks and homegrown extremists that pose increased risks to Americans, he said.