ANNAPOLIS -- Roosevelt Moore, manager of Takoma Liquors in the District, can barely hold back a wry smile at the thought that the Maryland General Assembly may bestow upon him an indirect form of financial aid.

Moore, whose Eastern Avenue Liquor store is across the street from the Prince George's County line, believes he stands to reap a virtual bonanza if the lawmakers vote this year to raise the state's drinking age to 21.

Asked if a higher drinking age in Maryland would bring new customers to his liquor store in Washington, where the legal age for buying alcoholic beverages is 18, Moore replied, "Hell, yes!"

"We're right across the street," Moore said. "If we get the (lottery) numbers in D.C., plus the 21-year-old drinking age in Maryland, we'll get all the business."

Moore's glee at the thought of Maryland's young adults flocking across the District line to buy their spirits reaches to the heart of the economic argument against increasing the state's drinking age. With the District now hoping to start its own lottery soon-- beginning with the popular instant rub-off game--Maryland liquor stores near the border already are bracing for a loss of lottery sales estimated as high as $30 million a year, or 1 percent of the state's total lottery revenue.

Lottery outlets on the border serving Washington customers account for 20 percent of the state's lottery revenues, according to state government statistics. Raising the drinking age in addition would constitute a one-two punch to those border businesses, most of which are liquor and food stores already in intense competition with District establishments.

"The D.C. liquor dealers are licking their chops over the prospect of increased business," said Del. Thomas J. Mooney, a vocal opponent of the higher drinking age. Mooney's Prince George's County district includes parts of College Park and the University of Maryland, where owners of campus taverns stand to lose their principal clientele--the students--if the higher age is enacted.

"I don't think it's going to stop a single fatality. It will hurt the small liquor businesses, and it will line the coffers of the D.C. governnment," Mooney said. "It's a great case of symbolic gratification."

Last year, and in past sessions, those arguments were persuasive enough to keep a higher drinking age from becoming law. The issue reached a stalemate in the House of Delegates last year because of the near-total opposition of the Prince George's County delegation, many of whom reported intense lobbying from county tavern owners.

This year, however, even the opponents of a higher drinking age, like Mooney, expect the measure to pass, in part because of some noted defections from the county's nearly united front. But also this year, proponents of raising the drinking age came to the state house armed with a persuasive set of numbers, a litany of drunk-driving horror stories, and heightened public concern on their side.

"I'll go for 21," said Del. Gerard F. Devlin (D-Prince George's), who held out for 19 last year but decided to back 21 because "there's a lot of concern among my constituents. We had 20 kids killed in Bowie in 1980," he said.

"I think it will pass out of a sense of desperation because of the carnage on the roads," Mooney said.

The numbers are formidable. Del. Charles Kountz (D-Baltimore County) said this week that in 1973, the last year the legal drinking age in Maryland was 21, 799 alcohol-related auto accidents were reported among the 15- to 18-year-old age group. By comparison, 1,772 such accidents were reported among the same age group last year.

William T.S. Bricker, director of the state's Motor Vehicle Administration and chairman of a task force on drunk driving, cited insurance company statistics showing that in six states where the drinking age was raised, alcohol-related traffic deaths decreased by an average of 28 percent.

Those new figures were enough to prompt Gov. Harry Hughes, an opponent last year of raising the age to 21, to concede now that he is "predisposed" to the 21-year-old drinking age, although he has not yet taken an official position.

The change is also being supported by Del. Joseph E. Owens (D-Montgomery), the hardline chairman of the Judiciary Committee whose support is considered crucial for any piece of legislation ever to see the light of day from his committee.

Owens, whose committee last year supported the 21-year-old drinking age, said he was not concerned about young people driving into the District to drink, since many of them did so anyway and since the vast majority of Maryland's youth lived too far away. Also, Owens added, many tavern owners themselves preferred older, more settled clientele to the often-rowdy 18-, 19- and 20-year-old campus set.

The change in the drinking age also is backed by Mothers Against Drunk Drivers, a national organization founded in Maryland.

Mooney was more pessimistic about the impact of raising the age, insisting instead that the younger adults would still drink.

"When I grew up, it was 21," he said, sitting after hours in his second-floor office and popping the pull tab from a cold Lite beer on his desk. "You could always get a fake I.D. This bill will just help the printers."