There's a few logical measures that would probably be implemented:
Shut down all travel
Shut down international and internal travel to the greatest extent possible.
I'm talking about closing borders, barricading highways, grounding, or turning away any international flights, quarantining any international travelers that have no way of returning to their countries of origin, and threatening to shoot down any planes that may seek to violate the US's airspace (and actually doing so if they try to land on American soil).
NOTE: In the case of the United States you actually face a fairly big threat in the form of the southern border. Mexico has a large population, and poor governmental organization. I could easily imagine hordes of fleeing civilians and millions of zombies crossing north into the USA. Canada is not quite the same situation because the population is a lot smaller, the military fairly organized, the great lakes comprise a large part of the border, and most Canadians would probably just flee north, not south.
Any cruise ships, etc. that carry supplies and can support their passengers for an extended period of time would be instructed to put out to sea, or not come in contact with the mainland. Supplies would eventually be dropped off to them, such that they do not become infected.
Martial law is an absolute given in this situation as well. By far the best thing to do would be to clear the streets with brutal efficiency. Riots and civil unrest and almost a given in a "end of times" situation. Panicked people will go out in the streets demanding government action, and will promptly become zombie fodder. You want to avoid that at all costs, as it causes needless destruction, casualties, and distracts the military and law enforcement from the issue at hand - killing zombies.
Deploy all armed forces
Immediately recall/activate all military personnel, and bring overseas forces home ASAP. Every soldier capable of following orders and shooting a gun should be deployed. I'm talking about mobilizing even relatively green recruits in various rear-echelon activities.
A tank can crush an entire mob of zombies with ease, but it needs a secure base from which to operate, and rearm, and it can't clear buildings - that's where grunts come in.
Implement bio-hazard containment measures
This implies that the leadership of the country is evacuated to various bunkers such that you don't lose chain of command.
Military units would be issued MOP gear where available, and be advised as to how to handle wounded. Something that has to be underlined here is that you face a huge potential discipline and moral issue when it becomes apparent that wounded (even only lightly wounded) individuals must essentially be put down.
No man is going to sit by and watch a soldier put their wife of child down. No soldier will willingly put their buddy down unless they have a very through and clear understanding of what's going on. And unfortunately you can't afford the luxury of letting these people learn from their mistakes.
You'll probably need to implement holding camps for the wounded where you can let their condition run its course, and then put them down. You'll want to hold that secret from the public, etc.
Spread the news
Disinformation and ignorance and big enemies in this fight. Advisories must be put out as to how people can become infected, and as to how a zombie must be brought down and disposed of.
The american public is comprised of a large number of armed individuals who may be able to effectively defend their homes/neighborhoods if they realize what they're dealing with.
You'll probably also want to advise people to barricade themselves in their homes, and keep quiet. This might actually not always be the best thing for them to do, but it helps the authorities. If a family is cornered and killed in their home, there's a chance that the zombies will remain localized in that one place. If the family goes on the run and pulls a horde of zombie into the woods in hot pursuit, you now have a much more difficult clean-up situation on your hands.
A great emphasis should be put on informing law enforcement agencies and emergency crews as to how to handle infected citizens, and to protect themselves of bites and scratches. You don't want firefighters and paramedics dying in the first few confusing hours of the crisis as they're trying to help a "wounded civilian". In fact, realize that fires may consume entire cities in the chaos that will likely ensue, and those firefighters will be needed to save critical infrastructure such as power plants, supply depots, train stations, etc.
Be prepared for extreme measures
Unfortunately all this looks good on paper, but is bound to screw up in real life. Simply accept it. Civilians will attempt to break through army barricades in a horde of panicked people and zombies.
Not if, but when this happens, you must be prepared and have assets in place to stop that horde from escaping population centers, or entering the country as I mentioned in the Mexico example.
Deploy heavy duty bombs (napalm, air burst, etc.), or even nukes if you have to. Have military units mow down entire crowds. Those who make it out in time, or sit tight to be rescued will be spared. Those who pose a threat, and may spread the disease must be eliminated.
To this end you may even wish to have key individuals or units in charge of certain operations.
Lemme know if you'd like more detail in one area or another.