A variety of changes in the laws of Maryland and Virginia take place today, including one that should be immediately noticeable - implementation of Maryland's right on red law.

The law, which allows motorists to turn right at most red lights after coming to a complete stop, makes Maryland consistent with Virginia and 46 other states. Virginia passed similar legislation in 1976.

Congress has required all states to adopt right on red by today or lose certain federal funds, but the District of Columbia has been granted a one-month extension while federal officials debate whether the city will be allowed to adopt a more conservative approach that would permit motorists to turn right on red only at designated intersections.

Right on red became law in Maryland in 1977, but implementation of the law was delayed until July 1, 1978, to allow traffic engineers time to study Maryland's intersections.

About 20 percent of the state's intersections, which are considered too dangerous or where pedestrian traffic is too heavy, will be marked with "No Right on Red" signs.

In Montgomery County, a law requiring at least one smoke detector in each sleeping area of a house or apartment takes effect today. The law also requires smoke detectors to be installed in each stairway leading to an occupied part of a home. Only residents of Rockville and Gaithesburg are exempt from the law, which carries a fine of up to $1,000 and up to six months in jail for failure to comply.

In Virginia, changes in the law effective today include a new law requiring insurance companies to explain why they refuse coverage or terminate policies and how they calculate underwriting decisions.

"Often, our consumer protection division has found that people have been put into an assigned risk category, have had their premiums increased drastically or have been cancelled - and not been told why." Attorney General J. Marshall Coleman said. That will change, he said.

Other new laws in Virginia extend coverage of oil spill laws to land vehicles as well as seagoing vessels, allow bar and restaurant patrons to drink standing up as well as seated and limit the use of recorded telephone solicitations to those that may be disconnected by the recipient.

Still other Virginia laws taking effect today allow police to take custody of children who are without adult supervision if an officer believes the child's welfare is in jeopardy, exempt motor vehicle, boat and airplane repair firms from Sunday closing laws and allow local governments to restrict water use during emergencies.

In Maryland, uninsured motorists today face a higher penalty for their failure to get insurance - up to $100 from a previous ceiling of $60.

Also in Maryland, changes in tax laws increase the amount of pension income exclude from taxable income and allow working parents to take credit for part or all of the expense of day care when figuring their Maryland taxable income. A special student filing status has been eliminated from tax regulations which means students don't have to file a return unless they have income equal to the federal filing requirement for a single person ($2.950 in 1977).