The White House may not acknowledge this day (nothing on their website.) Despite this break with tradition by the current administration, I know most of us don't need any politician's blessing to pray to whatever God we believe in:
2009 Prayer for Our Nation
Father in Heaven,
We lift our eyes toward Your Throne, where You reign in righteousness.
Your Word assures us that when Your people cry out in sincerity and humility, You will never turn a deaf ear to us.
We call upon You now, seeking Your forgiveness and favor.
Look over this fevered landscape and heal us, Lord.
Drop knees to the floor and raise eyes to the sky, for we know where our help comes from.
Unite these States again in devotion to You, and blur every dividing line.
Do not give us over to our sins. Give us, instead, over to passionate prayer that moves Your heart.
“May Your unfailing love rest upon us, O Lord, even as we put our hope in You.”
In the Name of our Lord and Savior, Jesus Christ
Source for this prayer, and more information as to how you can participate, go here.