You're right. The 2001 Statistical Abstract has federal spending at 1864 billion, total GDP at 10,082 billion.
I had remembered often seeing the Wall Street Journal editorial page claim that income taxes to GDP were typically 17-20% of GDP, and thought that Social Security taxes and borrowing would have pushed it over 25%, but evidently not.
Whether I did actually see the WSJ say that before my memory lost some of its youthful vigor is another matter, of course.
I wonder what the figure would be after five (or 20) years of GOP dominance of the fedgov.