Virginians who smoke marijuana, play bingo or buy a pet could be affected by new laws that become effective today.

The laws were created by the 738 bills passed by the 1979 General Assembly and signed by Gov. John N. Dalton. Almost all of the bills take effect today.

One of the new measures relaxes marijuana laws somewhat, reducing the penalty for the first conviction for possession of marijuana to a maximum of 30 days in jail, or a $500 fine or both. Current Virginia law carries a fine of up to $1,000 or one year in jail, or both.

The sale of one-half ounce or less of marijuana will become a Class I misdeameanor instead of a felony, and the legal definition of "manufacturing" the drug will be modified so a person growing a few plants is not subject to the same felony penalties as someone in business of growing marijuana.

The legislation will also permit doctors to perscribe marijuana in special cases.

The new bingo law is designed to prevent a recurrence of the bingo scandals that have been reported in Northern Verginia. The law tightens financial reporting standards for operators of bingo games and restricts the number of days they can operate. It also gives localities the option of allowing "instant bingo."

Another law will go into effect today will give consumers the right to get a replacement or their money back if pet dealers sell them sick animals.

A petroleum products franchise act will also go into effect, preventing oil companies from opening a company-operated station within one and a half miles of a franchised dealer station. Such dealers lease stations from oil companies and are not company employes.

Other laws going into effect today include:

An automobile repair facilities act that will require written estimates at the time vehicles are brought in for service.

An act requiring officers of public utilities to disclose certain financial interests.

Physicians must obtain the written consent of pregnant women before performing abortions.

A foreigner who acquires land in Virginia must submit a report to the state Commission of Agriculture and Consumer Services within 90 days of the transaction.