President Obama gestures as he answers questions from members of the media during a news conference Friday in the State Dining Room of the White House. (Pablo Martinez Monsivais/AP)

President Obama has decided not to directly confront Russia over its new air offensive in Syria, believing that President Vladi­mir Putin will soon find himself in a Syrian “quagmire,” but he has approved a new escalation of U.S. efforts against the Islamic State.

Obama laid out the U.S. response to Russia’s actions during a meeting with senior aides Thursday evening. Details were firmed up in a meeting Friday morning among national security principals at the White House, senior administration officials said.

At the same time, the president also approved proposals, made prior to this week’s Russian actions, to strengthen the U.S. fight against the militants. Those measures were recommended by Obama’s new Joint Chiefs of Staff chairman, Gen. Joseph F. Dunford Jr.

They include direct U.S. weapons shipments, overland from Iraq, to Syrian Kurdish and Arab fighters who in recent months have pushed the Islamic State from a major portion of northern Syria along the Turkish border.

The Kurds are now expected to begin moving south toward Raqqa, the de facto militant capital, in north-central Syria.

U.S. airstrikes are also slated to increase west of the Euphrates, where U.S.-backed opposition forces have had little recent success against the Islamic State. Those strikes are being launched from Incirlik air base in Turkey, where aircraft from other coalition partners will join U.S. planes.

Far from attacking the Islamic State, as Russia has said it intends, its three days of airstrikes appear to have focused largely on opposition forces, some of them U.S.-backed, that are fighting across western Syria against the army of President Bashar al-
Assad, whose government is backed by Moscow.

Obama did not respond directly to questions about what, if anything, he would do to help the embattled opposition, which includes thousands of fighters who have been trained and armed over the years by the CIA, as well as non-Islamic State extremists. Senior administration officials said that training and limited supplies for those inside Syria would continue but that the policy was likely to continue.

Current and former U.S. officials voiced concern that the Russian bombing would damage a covert program already struggling to gain traction in the fight against Assad. It is also likely to increase frustration among the rebels “that the Americans don’t do as much as the Russians do for their side of the conflict,” said Robert Ford, the former U.S. ambassador to Syria who resigned that position in part out of frustration with administration policy.

Rep. Adam Schiff (Calif.), the ranking Democrat on the House Intelligence Committee, said the Russian move “really ups the ante for the United States. We do have great reputational costs in letting the Russians assert themselves and be seen as a more forceful actor on the ground in Syria. We also have a deep interest in protecting the moderate population, and that’s going to push us to have greater involvement, which is a risky proposition.”

Any direct military response against Russia, a U.S. military official said, would probably require new presidential authorities. But Obama, speaking at a White House news conference Friday, made it clear that he has no intention of directly confronting Russian forces.

“We’re not going to make Syria into a proxy war between the United States and Russia. That would be a bad strategy on our part,” Obama said. “This is a battle between Russia, Iran and Assad against the overwhelming majority of the Syrian people. Our battle is with ISIL,” he said, referring to the Islamic State.

Obama responded angrily to suggestions of U.S. weakness in the face of Russian aggression, including Putin’s decision to launch surprise airstrikes just two days after meeting with Obama at the United Nations.

“This is not some superpower chessboard contest,” Obama said. “Mr. Putin had to go into Syria not out of strength but out of weakness, because his client, Mr. Assad, was crumbling.”

Rather than building support for Assad, a minority ruler, Russia would alienate Syria’s Sunni majority and the Sunni-ruled countries in the region he has been trying to court, Obama said.

The president said this “attempt by Russia and Iran,” the regime’s other backer, “to prop up Assad and try to pacify the population is just going to get them stuck in a quagmire. And it won’t work. And they will be there for a while if they don’t take a different course.”

At least one senior Russian official noted that Russia had learned during its ill-fated occupation of Afghanistan during the 1980s that airstrikes are not enough to hold territory — a lesson the United States has also learned more recently in both Syria and Iraq.

Without an immediate ground operation by the weakened Syrian army to capture bombed opposition territory, “the results of these airstrikes will be brought to naught,” Gen. Makhmut Gareyev, president of the Academy of Military Sciences, said, according to the Russian news agency Interfax.

In a conversation Thursday between the U.S. Defense Department and Russia’s Defense Ministry, arranged to “de-conflict” the countries’ air operations over Syria and avoid a possible collision, the Russians requested U.S. intelligence on possible Islamic State targets, according to a senior administration official, one of several who discussed internal discussions on the condition of anonymity.

“The answer we gave is that we cannot coordinate with you if you’re fighting the Syrian opposition. . . . We’re not going to make their task any easier if their fight is the wrong fight,” the official said. During their U.N. conversation, the official said, Obama told Putin that “if you’re not interested” in fighting the Islamic State, “what type of possible engagement could there be” between them? In his news conference, Obama also defended his decisions to not directly intervene in Syria’s civil war over the past four years. “And when I hear people offering up half-baked ideas as if they are solutions, or trying to downplay the challenges involved in this situation — what I’d like to see people ask is, specifically, precisely, what exactly would you do, and how would you fund it, and how would you sustain it?

“And typically, what you get is a bunch of mumbo jumbo,” he said.

“We are going to continue to go after ISIL. We are going to continue to reach out to a moderate opposition,” Obama said.

The CIA has provided the thousands of fighters it has trained at secret bases in Jordan with communications equipment, intelligence support and arms, including antitank missiles. Those CIA-backed fighters reentered Syria across that country’s southern border with Jordan, but many have made their way into units that are now arrayed north and east of Damascus — areas that have been pounded by Russian strikes over the past several days.

A former senior U.S. intelligence official said the U.S. failure to respond to the strikes or bolster support for CIA-trained units is likely to anger CIA paramilitary teams in the region that have for several years chafed at White House-imposed limits on the level of support given to moderate rebel groups.

“There is a huge amount of frustration with the indecision and ability to commit by this administration,” said a former senior U.S. intelligence official with extensive experience in the Middle East. “The agency has a problem,” the former official said. U.S.-backed fighters “look at the CIA or DOD trainers as reflecting the U.S. government. They believe that we know what’s going on and can influence what’s going on. If we’re not influencing it, it makes them insecure. They will defect, go home or join the refugee stream heading to Europe.”

The current and former officials also expressed concern that the Russian strikes would prompt rebel groups to intensify their efforts to acquire antiaircraft weaponry, including ­surface-to-air missiles — munitions the United States has worked to keep out of Syria for fear that they would be seized by al-Qaeda or the Islamic State.

The CIA operation has largely avoided the blunders that have beset the separately run Pentagon effort to arm and train rebels to fight the Islamic State, a program that has seen its fighters quickly captured and surrendering their weapons to an al-Qaeda affiliate. Even so, the CIA program has failed to shift the course of the conflict in Syria, and ­agency-backed fighters have long complained about the U.S. refusal to provide more powerful weapons, air support or no-fly zones.

Former secretary of state Hillary Rodham Clinton, who is seeking the Democratic presidential nomination, said Thursday that the United States should create “no-fly zones” and “humanitarian corridors” to protect civilians and moderate anti-
Assad rebels in Syria.

Obama said Clinton “is not half-baked in terms of her approach to these problems.” But, he said, “there’s a difference between running for president and being president. And the decisions that are being made and the discussions that I’m having with the Joint Chiefs become much more specific and require, I think, a different kind of judgment.

“If and when she’s president, then she’ll make those judgments,” Obama said, adding that “these are tough calls.”

Missy Ryan and Steven Mufson contributed to this report.