OECD data (http://www.oecd.org/dataoecd/5/51/2483816.xls) indicates that for the Euro area, net Government Debt is 52.5% of GDP for 2003 compared to 42.8% of GDP for the US.
(For what it is worth, there is an extranenous ')' in the URL.)
One might keep in mind that debt is treated differently by different countries. For instance, if you look at table 32 (gross debt) rather than table 33 ("net" debt), you can see that the U.S. is at 62.5% versus the E.U. at 77.4% for 2003. [Gross debt in this case I believe attempts to simply lump together debt rather than follow each country's on-budget/off-budget rules and accounting for assets.]
Another item to look at is how much of a burden is the debt. Table 31 indicates that 3% of the GDP in E.U. is going to pay interest, whereas the U.S. is only at 1.8% (and Japan only at 1.5% despite their very large government debt due to the very low interest rates prevailing there.)