In order to be eligible for Fairfax County tax and rent relief for 1983, eligible senior citizens and permanently and totally disabled persons must file applications by May 1.

Personal property tax relief for senior citizens 65 or older and disabled citizens includes a total exemption of one auto per household and one mobile home, if it is used as a residence.

The county real estate tax exemption includes a total exemption from tax on an applicant's home and up to one acre of land it occupies. In addition, the county provides grants to senior and disabled citizens renting residences in which they live. The grant would equal 20 percent of the previous year's rent payments or $425, whichever is less.

To qualify for a real estate tax exemption or rental grant and personal property tax relief, the 1982 household gross income of the applicant, spouse and relatives living in a household cannot exceed $15,000, excluding the first $4,000 of income of each relative other than the spouse.

The combined financial net worth of an applicant and spouse living in the household must not be more than $65,000, excluding the value of the residence and up to one acre of land.

Applications and assistance in filling out the applications are available at the Office of Assessments on the third floor of the Massey Building and at branch assessment offices in the county.

Application forms also are available in Fairfax County libraries. For information, call 691-2437.