Applications for two Fairfax County programs -- housing expense relief and auto sticker cost exemption for senior and disabled residents -- must be filled with the Office of Assessments by midnight Dec. 31.

The Housing Expense Relief Program provides up to $150 per year to homeowners or renters between 55 and 64 years old, and to homeowners or renters with minor age children living at home.

To qualify, applicants must have a gross income from all sources of no more than $10,000 annually, excluding the first $4,000 of income of each relative other than the spouse residing in the household. The combined financial net worth of the applicant and spouse living in th household may not exceed $35,000, excluding the value of the residence, if owned, and up to one acre of land around it.

The Auto Sticker Cost Exemption Program makes auto stickers available free for persons 65 or older or persons who are permanently and totally disabled as Dec. 31. They must also be approved for either personal property, real estate tax exemption or a rental grant in 1980.

Applications are being accepted and assistance is available on the third floor of the Massey Building and the branch assessment offices at: Franconia, 6121 Franconia rd.; Groveton, 6210 North King Highway; Mason, 6507 Columbia Pike, Anndandale; McLean, 1437 Balls Hill Rd.; Reston, 11415 Isaac Newton Square South, and West Springfield, 6140 Rolling Road. Application forms are available at those locations and in public libraries. For more information, call 691-2437.