The fact that the announcement was made on the last stop of Mr. Obama’s weeklong Asian trip underscored the sense of urgency about fears that Russia was destabilizing eastern Ukraine. The European Union is expected to announce similar measures within a day or so, as Mr. Obama and European leaders strive to keep a united front in their campaign of pressure on Moscow.
“These sanctions represent the next stage in a calibrated effort to change Russia’s behavior,” Mr. Obama said in a news conference with President Benigno S. Aquino III of the Philippines.
But Mr. Obama acknowledged, “We don’t yet know whether it is going to work,” and left the door open to more sweeping sanctions against Russian industries like banking and defense.
Mr. Obama did not specify the names of the Russian individuals or entities on the latest blacklist. The White House and the Treasury Department were scheduled to offer details later on Monday.
Among the individuals likely to be listed are Igor I. Sechin, the president of the state-owned Rosneft oil company, and Aleksei B. Miller, the head of the state-owned energy giant Gazprom, American officials said.
Administration officials have said the sanctions would target individuals with ties to President Vladimir V. Putin, though Mr. Obama insisted that they were not intended to punish him.
“The goal is not to go after Mr. Putin personally; the goal is to change his calculus, to encourage him to walk the walk, not just talk the talk” when it comes to diplomatic efforts to resolve the crisis, Mr. Obama said.
Mr. Obama said the sanctions would affect high-tech military exports to Russia, because they are not “appropriate to be transferred in the current environment.”
Mr. Obama and Mr. Aquino also promoted a new 10-year agreement between the United States and the Philippines that would give American warships and planes extended access to bases here.
“This is going to be a terrific opportunity for us to work with the Philippines, to make sure our navies, our air forces are coordinating,” Mr. Obama said.
U.S. President Barack Obama, left, speaks as Philippine President Benigno Aquino III looks on during a joint news conference at Malacanang Palace in Manila
The Philippines has been embroiled in a dispute with China over scattered islands in the South China Sea, and the return of a visible American military presence here will send a signal to the Chinese that the United States will resist Chinese expansionism.
Still, Mr. Obama said that the agreement was not meant to counter or contain China, and he added, “it’s inevitable that China is going to be a dominant power in this region, just by sheer size.”
On Monday, however, Mr. Obama’s focus was as much on Russia as on China. He reiterated that the Group of 7 countries were united in their approach toward Mr. Putin. But there has been a debate within the administration about whether the United States should impose more sweeping sanctions even if Europe is reluctant to follow suit because of economic concerns.
The issue came to a head in recent days as American and European leaders tried to coordinate this new round of sanctions after the collapse of a Geneva agreement to de-escalate the crisis in Ukraine.
Secretary of State John Kerry delivered a blistering public attack on Moscow on Thursday night for not living up to the agreement, but the plan to follow that up with sanctions on Friday fell apart while Washington waited for Brussels, postponing action until Monday at the earliest.
The deliberations in the West came as pro-Russian forces in Ukraine on Sunday continued to defy international demands to stand down. An antigovernment militia paraded eight detained members of a European military observer mission before cameras, while protesters seized a regional government television station and declared that they would use it to air Russian newscasts.
The display of the captive European observers underscored the challenge for Washington and Brussels in defusing the conflict. The observers, who were seized at a checkpoint on Friday, were led into an auditorium in the eastern city of Slovyansk by masked gunmen. The self-appointed mayor refused to discuss conditions under which they might be released, beyond mentioning a prisoner exchange, although one of the observers was later freed for health reasons.
Also on Sunday, a crowd of pro-Russia militants proclaimed the “Lugansk People’s Republic” in Lugansk, which lies east of Donetsk near the Russian border. Video posted on the website of the Ukrainian service of Radio Liberty showed two unidentified women declaring the republic and announcing that a referendum would be held on May 11 that would allow the region to join neighboring Russia. A crowd of about 200 people cheered.
Yelena Bugayets, the head of the press service for the Lugansk regional council, dismissed the idea that the militants had any sway in the city.
The militants occupied the local headquarters of Ukraine’s secret service on April 6, she said, and since then have held regular meetings in front of it. But their proclamations have no practical effect, she insisted in a telephone interview.
While some of Mr. Obama’s advisers want him to impose sanctions against whole sectors of the Russian economy, the president has decided against it for now, cognizant of the resistance of European nations that have far more at stake economically, officials said. During internal deliberations, Jacob J. Lew, the secretary of the Treasury, and other officials have argued for caution, maintaining that, while action is needed, more expansive measures without European support might hurt American business interests without having the desired impact on Russia, according to people informed about the discussion.
Mr. Obama has been particularly intent on not getting too far in front of Europe to avoid giving Mr. Putin a chance to drive a wedge in the international coalition that has condemned the Russian annexation of Crimea and actions to destabilize eastern Ukraine.
“The notion that for us to go forward with sectoral sanctions on our own without the Europeans would be the most effective deterrent to Mr. Putin, I think, is factually wrong,” Mr. Obama told reporters on Sunday in Malaysia. “We’re going to be in a stronger position to deter Mr. Putin when he sees that the world is unified.”
“For example,” he added, “say we’re not going to allow certain arms sales to Russia — just to take an example — but every European defense contractor backfills what we do, then it’s not very effective.”
Some officials, however, privately argue that the administration has made coordinating with Europe too high a priority and that effectively deferring to the 28-member European Union is a recipe for inaction. The United States, these officials contend, should move ahead with more decisive action on the theory that Europe wants leadership from Washington and historically joins in eventually.
“While imposing sanctions together with the E.U. would be nice, the U.S. simply has to lead and not waste more time trying to present a united approach,” said David J. Kramer, the president of Freedom House, an advocacy group, and a former Bush administration official. “It’s easier for us to do so than it is for the Europeans, and they will follow, as long as we lead.”
A task force of specialists on Russia that includes Mr. Kramer sent the White House a list of possible targets for sanctions, including Russian officials and business leaders as well as nine of its most significant companies.
Senator Bob Corker of Tennessee, the ranking Republican on the Foreign Relations Committee, made a similar proposal. “Hitting four of the largest banks there would send shock waves into the economy; hitting Gazprom would certainly send shock waves into the economy,” he said Sunday on “Face the Nation” on CBS.
