For the first time since the Eisenhower era, Maryland Republicans are adding voters to their ranks 50 percent faster than the traditionally dominant Democrats, according to the most recent voter registration figures compiled by state election officials.

Part of this turnabout stems from the Maryland Republicans' increased ability to attract new voters: After years of watching the Democrats sign up three new voters for every one Republican convert, the Republicans in the last six months have drawn almost even with the Democrats in the race for new voters.

But more disturbing for the Democrats is the rapid reduction of their voting rolls in recent months. Unofficial registration figures for June 30 show Democrats disappearing from the voter rolls by the thousands, particularly in Baltimore City and some of its blue-collar suburbs.

As a result, in this presidential election year -- a time when voter rolls in both parties usually climb to an all-time high -- there are 4,000 fewer registered Democrats in Maryland than there were in the off-year 1978.

Republicans by contrast, have added more than 10,000 voters to their ranks in the last 21 months, according to the figures compiled by the State Board of Election Laws.

Election records dating back to 1956 indicate that never in that time have the state's Democrats suffered as dramatic a setback as in the last 21 months.

The unofficial election figures give little indication that the Democrats who have dropped off the rolls have switched their registration to Republican or independent. The party's voter decline, instead, appears to stem from a general turning away from the political process that is more pronounced among Maryland's Democrats than its Republicans.

The changes, while striking, have as yet had little effect on the overall political configuration of the state. Democrats still outnumber Republicans by about 2 1/2 to 1, while about 7 percent of the state's 1.9 million voters are registered as independents.

State Elections Board Commissioner Willard Morris also cautioned that a flood of as many as 100,000 new registrants can be expected to sign up before the Oct. 6 deadline.

Morris also noted that revisions in the election laws, which now require each local election board to do an annual purge of registrants who fail to vote for five years, may be partially responsible for the rapid fall-off of Democratic voters in places like Baltimore City.

The city, a Democratic stronghold which has been rapidly losing population in the past decade, lost nearly 9,000 voters in the past six months -- 99 percent of them Democrats. While Republicans are outnumbered there 9 to 1, Democratic voter losses in the city outstripped the Republicans' at a rate of 90 to 1.

To the south of Baltimore, in the rapidly growing county of Anne Arundel, the voting rolls were reduced by 5,000 in the last six months -- and the Democrats absorbed 80 percent of that loss.

However, according to Betty Eby, chief of staff of the Anne Arundel elections board, the voter fall-off tends to look more dramatic there because the county's system for eliminating voters from the rolls is more strict than the practices in most of Maryland's other 23 jurisdictions.

Nonetheless, the voters who are disappearing in the working-class areas of Baltimore and the blue-collar suburbs of northern Anne Arundel are the same Democrats whom President Carter needs to help him carry the state in November.

Elsewhere around the state, Republicans came close to matching Democrats 1 for 1 as voters were added to the rolls in the past six months.

In Montgomery County, nearly 7,000 Republican voters have been added to the rolls since Jan. 1, compared to 8,200 Democratas. In Prince George's, Democrats continued to increase their voter lists twice as fast as the Republicans.

Statewide, Republicans have increased their numbers by more than 19,000 voters in the past six months, while Democrats added slightly more than 12,000 -- a 50 percent registration edge for the Republicans. In the period, independents increased their ranks by about 6,000 voters.

One indication of the comparative decline in the Democrats' appeal this year is their failure -- so far -- to pull back the voters who have drifted away since the last presidential election. With Carter on the verge of his first nomination on July 31, 1976, Maryland Democrats had wooed back all but 7,000 of the voters who had fallen away since November 1972.

This year, the June 30 figures show nearly 50,000 fewer Democrats registered in the state than there were in November 1976.

Republicans, who suffered heavy voter losses in the years betweeen 1974 and 1978, are also nearly 22,000 voters below their November 1976 totals, but they are making up for lost ground much faster than the Democrats.

Independent voters, by contrast, are now more numerous than ever before -- there are 127,510 of them registered statewide, nearly one-third of these living in Montgomery County.

Republican Party Chairman Allan Levey was predictably gleeful at the latest turn of events, which he attributed to voter dissatisfaction with Carter's economic and foreign policies and a growing distrust of the heavily Democratic Congress.

"Also there's been tremendous work been done by our county central committees on registration," Levey said. "These three things are beginning to pay off."