An article Monday incorrectly stated that a new Maryland law allowing seven-digit vanity plates for automobiles went into effect July 1. That law becomes effective Jan. 1, 1986.

If you're planning to sip a cold one while driving home from work today, be advised that the practice is now illegal in Maryland.

And if you've been prevented from getting vanity license plates for your car because of the existing limit of six letters and numerals, as of today, you'll have seven spaces to get your message across.

From the monumental to the mundane, today is the day that 648 of the 882 laws enacted by the 1985 General Assembly and signed by Gov. Harry Hughes go into effect. Many will go largely unnoticed by Maryland's 4 million citizens, but a number will have a major impact.

Among the latter are laws dealing with drinking alcohol and driving, both of which had been sought for years and ultimately passed this year as the legislature continued its assault on drunk drivers.

Not only will drinking while driving be prohibited, but drivers convicted of a drunk-driving offense twice in three years will face mandatory sentences of 48 hours in jail or 10 days of community service.

Children will be the beneficiaries of several new laws designed to protect them from abuse and exploitation, part of what Hughes dubbed his "youth initiative" during the 1985 session of the legislature. Several of those laws dealing with child abuse went into effect on June 1.

One of those going into effect today will have an immediate effect on the thousands of parents statewide who are delinquent in making child-support payments by requiring the automatic placement of liens on the paychecks of those who are more than 30 days in arrears.

Other new laws make it easier for children to testify in criminal trials, and establish a clearinghouse for information on missing children.

In the better-late-than-never category come several new statutes designed to strengthen the state's regulation of its savings and loan institutions, which might have forestalled the May crisis in the thrift industry had they been in effect.

Beginning today, the state division of savings and loan has the power to order thrifts to stop engaging in unsafe practices and to order the removal of any officer or director for unsound practices. Also, thrifts will be required to publish annual statements of financial condition.

Two other laws promise fundamentally to reshape the state's banking industry by permitting banks in the District of Columbia and 14 eastern states to merge with or acquire Maryland banks by 1987, beginning with a phase-in period this year. A separate measure, known as the Citicorp bill, allows out-of-state banks, including giant New York institutions, to establish Maryland branches if they meet certain investment and job-creation requirements.

Another business getting a boost will be the state's racing industry, which today begins benefiting from a $12 million tax break enacted by the assembly, at least part of which will begin showing up in larger purses and track amenities.

Also beginning today, the state Parole Commission must begin notifying crime victims or their families of the release of prisoners if requested to do so, and hazing by fraternities and sororities is outlawed and punishable by a fine of up to $500 and six months in jail. Crime victims also can now sit in on trials.

Maryland law will also begin to recognize so-called "living wills" under which persons may request that no extraordinary life-sustaining medical procedures be used on them if they are terminally ill.

Also, the state will be barred from investing pension funds in companies doing business in South Africa if the firms discriminate against blacks in their South African facilities.