Grump does make a good point about 'owned'.
I guess the Chinese can say that to us? 
I was just reading something about this the other day. The % of US debt owned by the Chinese isn't actually that high.
You're right, they're only about fifth or sixth as I recall.
I thought I posted the numbers on here but it may have been another site...
The numbers vary by how you calculate it, and actually this has China as the largest holder of foreign debt which is a substantial amount
As of January 2011, foreigners owned $4.45 trillion of U.S. debt, or approximately 47% of the debt held by the public of $9.49 trillion and 32% of the total debt of $14.1 trillion.[53] The largest holders were the central banks of China, Japan, the United Kingdom and Brazil.[55] The share held by foreign governments has grown over time, rising from 13% of the public debt in 1988[56] to 25% in 2007.[57]
As of May 2011 the largest single holder of U.S. government debt was China, with 36 percent of all foreign-held U.S. Treasury securities (16% of total US public debt).[58] China's holdings of government debt, as a percentage of all foreign-held government debt, have decreased a bit over the last year, but are up significantly since 2000 (when China held just 6 percent of all foreign-held U.S. Treasury securities).[59]
http://en.wikipedia.org/wiki/United_States_public_debtI'll revisit tomorrow as it is getting late.