A revision in the way standard metropolitan statistical areas are defined is expected to change parts of Washington's exurbia into suburbia some time after 1982, ading at least two Maryland counties to the area's domain.

Almost certain to join the newly defined region are Federick and Calvert counties, with St. Mary's and Howard counties in Maryland and Stafford County in Virginia less certain but possible additions to the federally defined metropolitan area.

"It's kind of a continuation of waht we've been experiencing, where people have been moving out to the fringe but having jobs close to the center," said John McClean, chief of data and forecasts for the Metropolitan Washington Council of Governments.

"In 1970, it was considered a 50-50 proposition whether Frederick County (out Interstate 270 north of Gaithersburg) would go to Baltimore or Washington's SMSA, but with the development of the 270 corridor, a lot of county people are working in Montgomery County. It's now solidly Washington's," said McClean. "In Calvert, there's similar traveling into the Washington area," he added.

The changes will take place after federal analysts look at data to determine whether 15 percent of the workers n outlying counties commute to central counties in the SMSA. Central counties recently have been redefined to include Montgomery and Prince George's counties, a change that makes the inclusion of Frederick and Calvert counties almost certain.

Much further down the road may be a consolidation of the Washington SMSA with the Baltimore SMSA, a change that would be of major proportions, adding two million or more persons to the area. The two areas recently have undertaken some common marketing efforts and are growning closer, but merger is still a long way off, analysts said.

Less drastic is the expected expansion to Frederick and Calvert, which would add fewer than 200,000 persons to the D.C. area, according to Richard Forstall, a Bureau of the Census representative to the federal interagency committee on SMSAs. "The percentage effect on an area the size of Washington obviously would not be very great," Forstall said.

Where the change would be felt most would be in the counties themselves.

Besides giving up whatever image they may have as rural areas, the counties will find themselves newly defined as metropolitan for the purpose of several federal grant-giving programs that proportion federal funds between metropolitan and nonmetropolitan areas.

Getting federal grants frequently "depends on the size of the pot and who you're competing with for it," said James Shaw, director of Frederick County's planning commission. "If we're just competing with nonmetropolitan counties, maybe we have some advantages," he said Shaw noted that larger, more urban counties frequently bring more staff and more expertise to the game of grantsmanship.

"Maybe to get the same or less money, we may have to devote more staff and time to compete with the big boys," said Shaw.

Shaw said his office already has been getting calls from the Metropolitan Washington COG, and that a benefit of Frederick's newly defined status may be increased cooperation and coordination with the Washington metropolitan area. But he noted that neighboring Carroll County, Md., has had some difficulties as part of a Baltimore regional planning group.

"In some ways it can be viewed as parochial, perhaps, but there's always a question about whether the larger region is looking out for your best interest," Shaw said. "Do you really get the importance when you're a small cog in a big wheel?"

In fact, at least one Maryland county, Charles, has kept its distance in spite of being included in the Washington SMSA. Instead of joining the Washington Metropolitan COG, Charles County has remained part of a tricounty planning agency in Southern Maryland.

Perhaps the stickiest question that will face the interagency committee on SMSAs down the road will be what to do with Howard County, now part of the Baltimore SMSA. The key is the new town, Columbia, where substantial numbers of residents commute in each direction. If the figures reveal that more commuters are heading south toward Washington, the committee will have to consider the unusual step of transferring the county from one SMSA to another.