Applications for help with housing expenses must be filed with the Fairfax County Office of Assessments by midnight Dec. 31.

The county's Housing Expense Relief program provides up to $150 per year in grants to qualifying low income homeowners or renters between 55 and 64 years old, and to low-income homeowners or renters of any age who have children who are minors 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 living in the home.

In addition, the combined financial net worth of the applicant and spouse living in the home may not exceed $35,000, excluding the value of the home, if owned, and up to one acre of land.

Applications are being accepted and assistance is available on the third floor of the Massey Building and the Branch Assessment offices at 6121 Franconia Rd., Franconia; 2511 Parkers La., Alexandria; 6507 Columbia Pike, Annandale; 1437 Balls Hill Rd., McLean; 11415 Isaac Newton Square South, Reston, and 6140 Rolling Rd., Springfield. Application forms are available at those locations and at county public libraries.

Another county program provides real estate tax or rent relief for senior citizens and for totally disabled people. Applications for that program may be submitted between Jan. 1 and May 1, 1983.

For information on either program, call 691-2437.