Montgomery County Council members, now elected at large, moved one step closer to election by district this week when the county's House delegation voted to allow the question to be placed on the 1982 ballot.

The delegates' action struck a blow at the Montgomery Democratic Party, which has fought the measure for more than a decade. The bill, which would allow voters to approve an amendment to the state constitution, still must be passed by the county's Senate delegation and the General Assembly.

If the measure eventually is approved, as expected, observers feel it is inevitable that Republicans and northern county residents stand a better chance of winning seats in the heavily Democratic county. The present seven council members all are Democrats.

Under the current rules, five of the council members must each live in a different district and two can live anywhere, but all are elected by all the voters. The amendment would allow voters to decide whether they approve the concept of election by district, and if so, what type of district elections should be held.

Although the amendment passed the 19-member House delegation unanimously, the affirmative vote probably was the most reluctant of this year's legislative session. The amendment has come unsuccessfully before the delegation for 12 years, but this year a strong umbrella group of civic and social organizations banded together to lobby the delegation for its approval. During the discussion before the vote, several delegates expressed continued opposition to the bill and admitted that the only reason they decided to support it was their belief that approval of this or a similar measure was inevitable.

Led by Del. Judith Toth (D-Bethesda), a member of what has been termed the reform faction of the delegation, the umbrella group put the delegates on notice that the amendment would become an election-year issue. Under the bombardment of constant pressure, delegate opposition began to crumble quickly.

The amendment, which now must go to the county Senate delegation, probably will be rewritten a number of times. The current measure was rehashed for more than two months before last night's session and is confusing.

If the bill passes, the voters will be asked in 1982 whether they want the state constitution to be changed to give them the choice of deciding on council member election by district. Then in the 1984 primary, voters will be asked whether they want election by districts; if they do, they then will choose between plans presented in the 1984 general election. One of the election plans will be written by a special charter commission selected by the County Council and the county executive. If a citizen wants to be on the commission, however, he or she can have his or her name placed on the 1984 primary ballot. If citizens want other election plans to be considered they can petition the proposals onto the ballot.

If no plan is approved in the 1984 general election, the process starts again in 1988 and runs out in 1990. If the process is concluded as quickly as possible, council members could be elected by district in 1986.