Elderly citizens who find real estate taxes or rent payments taking more and more of their fixed incomes, leaving less and less for food and other necessities, may find help in new legislation designed to provide relief.

All real estate taxes are expected to be somewhat lower this year because of state legislation reducing the allowable assessment base from 50 percent to 45 percent of market value. In addition, both Montgomery and Prince George's counties have reduced their tax rates.

For many homeowners on low, fixed incomes these provisions may fall short of what is needed. Consequently, additional help is provided by the Maryland homeowners tax credit program, which replaces the circuit breaker program of the past several years. While the new law applies to all homeowners, it provides a larger credit for those over 60 and for the disabled.

In general, the law is designed to provide the greatest relief to the most needy by relating taxes to income and ability to pay. The system involves a kind of alternate tax calculation that is usually less than that of the standard, rate-times-assessed-valuation system. The difference, up to a maximum of $900, is the tax credit.

To be eligible, applicants must have a legal owner's interest in the dwelling and it must be the applicant's principal residence. Combined net worth cannot be more than $200,000. A surviving spouse, if the deceased spouse qualified, does not need to meet the age requirement. If these conditions are met, it should be worthwhile to obtain an application and proceed as directed to determine any tax credit.

The purpose of the tax credit program is to provide help to those who need so they can keep their homes despite rising expenses. Applying for a tax credit is not a tax evasion measure, and all eligible homeowners are entitled to apply. The deadline for applying has been extended this year from Sept. 1 to Oct. 1.

Although the tax credit program is state administered, information is available through county revenue offices. In Montgomery County, the number to call is 279-1302; in Prince George's County, the number is 952-4040. These offices will mail an application form and information sheet upon request. They also can supply any explanation needed for completing the application.

There are similar programs for persons who rent their homes. Rent rebate or rent supplement programs are provided by countries rather than the state and therefore some local variations exist. In general, rent relief is designed to help persons on low incomes, the elderly and the handicapped.

In Prince George's County a rent rebate of 15 percent, up to a maximum of $232 a year, is provided qualifying county residents over 63 years of age. The law specifies a limit of $8,000 in combined net household income, excluding Social Security payments and railroad benefits or government pensions not to exceed $3,200 for each pensioned resident. Applicants must occupy the dwelling specified in the application. Net worth is limited to $150,000.

Application forms and information about the program are available from the Prince George's accounting office, telephone 952-3770. Sept. 1 is the deadline for filling an application covering the fiscal year from July 1, 1977, to June 30, 1978. Applications for the first six months of the current fiscal year will be accepted in December.

Montgomery County has just revised its program as reported in The Washington Post on July 12. All tenants with total incomes of less than $10,480 whose housing is not already subsidized and whose net worth is not more than $150,000 may be eligible, and should apply. The law provides a larger supplement for persons over 62, up to a maximum of $435 the year.

Because the Montgomery County rent supplement legislation has just been revised and its implementation is still to be worked out, inquires should be made to Information and Referral, telephone 279-1900. The usual Sept. 1 deadline may be extended, but application should not be delayed. Don Lazas, of the revenue office, said he believes that a number of eligible persons are unaware of benefits they need and to which they are entitled.