Transcript for The Syria Plan of Attack

night and the world was watching today as two rivals came face to face, president obama and vladimir putin of russia. The question was looming. What will russia do if the u.S. Launches a military strike on syria. Tonight abc news is learning that strike could be a lot bigger than we thought. Abc's chief white house correspondent jonathan karl is with the president tonight on the ground in russia. Reporter: President obama's first encounter here with vladimir putin lasted a scant 17 seconds. Smiles aside, the white house sees zero chance of changing russia's staunch opposition to attacking syria. Any progress on syria? We were talking about the economy. Reporter: Later mr. Obama headed to a dinner of world leaders nearly an hour late leaving him to take a long walk alone with leaders who will not take part on a military strike on syria. Alone or not, abc news has learned the president's national security team is preparing for a significantly larger military attack than most had anticipated. The air campaign which is expected to last at least two days will potentially include an aerial bombardment of missiles fired from b-2 and b-52 bombers flying from the united states. That in addition to a relentless assault from tomahawk missiles. Those ships ever loaded with nearly 200 missiles, plans call for firing the vast majority of them. As one senior national security official told abc news, this military strike could do more damage to assad's forces in 48 hours than the syrian rebels have done in nearly two years of civil war. That's more than president obama seemed to be suggesting just days ago. What we are envisioning is something limited. We send a shot across the bow staying stop doing this. Reporter: Diane, making things worse tonight, a new video obtained by the "new york times" that appears to show a group of syrian rebels executing a group of syrian soldiers in sold blood. It is the kind of activity, the kind of gruesomeness that makes it a lot harder to build support for the cause. Jon, if the vote were held tonight, is the president winning or losing his plan to get congressional approval for a strike? If congress were to hold a vote today, almost certainly it would fail. In fact, the abc news political unit has been counting votes in the house the magic number is 217 votes needed to either pass or fail. Take a look at this. Right now our political teams counts 217 house members either firmly no or leaning no, voting against the resolution. That doesn't mean it's over, but it sure looks bad right now for president obama and congress. So the president's got a lot of tough persuasion ahead if he can do this. Thank you so much, jon.

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