Automobile license tag renewal lines should be shorter, a few prescriptions may be cheaper and some evictions may be postponed for 90 days as the result of nearly two dozen bills acted on recently by Mayor Walter E. Washington.

One of the bills the mayor signed will allow him power to rotate the expiration date for auto tags in the city, all of which expire on March 1, thereby creating long lines of car owners waiting to renew their tags.

Under the new legislation, the mayor will be able to stagger the expiration dates throughout the year. He is expected to institute a system that would have tag expirations coincide with auto inspection deadlines, thus allowing a motorist to renew tags and inspection stickers simultaneously.

But because the legislation must still be acted on by Congress, a spokesman for the mayor said, the staggered renewal dates wil not go into effect until next year - after this year's long lines.

The mayor also signed legislation that would establish a committee within the department of human resources to regularly distribute a list of interchangeable prescription drugs available.

The bill is designed to give pharmacists a list of durgs tht could be substituted for prescribed drugs. The substitutes would have the same effect as the prescribed drug but may be cheaper. As a result of the legislation, its backers hope, consumers will be safeguarded against having to buy the most expensive brand drug simply because it was prescribed. Under the legislation, pharmacists would be required to offer the lower-priced substitute if is is available.

The may allowed to become law without his signature a bill that tightens the restrictions on mailing by city officials at public cost.

The legislation is aimed primarily at elected city officials and sets penalties of a $100 fine or up to a year in jail for violations and fines of up to $1,000 for willful violations.

Envelopes containing materials distributed at public cost must be stamped "official business" and no mass mailings may be made at public expense within 90 days of an election, the legislation states. No campaign materials may be contained on the publicly funded mailings, the bill reads, and telegrams may be sent at public expense only in emergency situations.

The mayor also allowed to become law without his signature emergency legislation that will prohibit for 90 days evictions for nonpayment of rent from properties owned by the redevelopment land agency. The enactment of the legislation means that any eviction or displacement notices for nonpayment received since Oct. 1 cannot be acted on for 90 days.

The mayor allowed to become law without his signature legislation aimed at restricting the amount of influence that large oil companies have in retail gasoline sales and increasing the power of local gasoline dealers.

The legislation would prohibit after Jan. 1, 1981, any refiners or producers from operating stations, and set strict guidelines governing the relationships between gasoline distributors and gasoline dealers.

Conversion of full service gasoline stations to limited service "gas and go" type operations wouldbe forbidden until after Jan. 1, 1979. At that time, the legislation says, a study of te effect of such limited service operations should have been studied by a city committee.

Council aides believe the gasoline legislation is almost certain to be challenged in court.

Among other legislation acted on by the mayor were the following bills:

Veto of a bill that would have exempted persons from paying the city's 12 per cent parking tax on parking that is park of their rent or within half a mile or their homes.

Emergency legislation requiring the city's alcoholic beverage control board to give Advisory Neighborhood Commissions a 30-day notice of all liquor license renewals and application hearings. It wil take effect without the mayors signature.

Revised legislation that clarifies previous language exempting certain property owners from the city's rent control law will become effective within out the mayor's signature. The revision allows only persons who own a single apartment building with four units or fewer to be exempt from rent control restrictions. Only if the four or fewer units are in one building and that building is the sole rental property owned is the exemption allowed.

All of the legislation except emergency bills must lay over in Congress for 30 days (while Congress is in session) before it becomes law.