Social Security Tax Hike Phaseout Act of 2004 - Amends the Internal Revenue Code to reduce from 85 to 60 percent the maximum applicable percentage of social security benefits includable in the gross income of a taxpayer. Phases in this reduction between 2005 and 2008. Appropriates to the Federal Hospital Insurance Trust Fund amounts equal to the reduction in revenues to the Treasury by reason of the enactment of this Act.