Estate Tax Deferral for Working Farms and Land Conservation Act of 2004 - Amends the Internal Revenue Code to exclude property used by a decedent's heir as farmland from the gross income of the decedent's estate. Imposes an additional estate tax if the decedent's heir disposes of such farmland or ceases to use it for farming purposes. Repeals the $500,000 limitation on the estate tax exclusion for land subject to a qualified conservation easement.