According to the Pew 2013 study, there are 5.3 million Jews in the United States, of which 10% claim to be Orthodox; at best this puts the Orthodox population at 530,000.
A good deal of the 5.3 million is not Jewish by halachic standards (due in large measure that 58% of Jewish marriages are Intermarriages) which would make the total Jewish population even less but the Orthodox percentage more.
Of the 10% claiming to be Orthodox, only 77% would avoid handling money on Shabbos. This would coincide with your statement that 77% of MO believe in G-d with absolute certainty.
So if we use the strictly Shomrei Torah and Mitzvos as the criteria for Orthodox, this brings the total orthodox population down to 408,000.
If your 2/3 number is correct, this would make the USA Hareidim population about 275,000.