Residents of Maryland's 5th Congressional District face a difficult task in today's primary election.

They must select the best Democrat to run against the best Republican in an election that will fill the seat vacated by Gladys Spellman's illness.

Thirty-one candidates campaigned vigorously for the two nominations. In addition to their own efforts, hundreds of volunteers engaged in telephoning and doorbell ringing on their behalf, and more than $400,000 was spent to buy radio and television time, newspaper space, leaflets and direct mail advertising for them.

One might think that an information blitz of such proportions would have two predictable consequences: It should generate interest that manifests itself in a heavy voter turnout, and it should give voters more than enough information on which to base an intelligent choice.

Unfortunately, political experts a turnout of only 22 percent of eligible voters. They say about 33,000 people will vote, but 121,000 others will not. If this forecast is correct, a mere 11,000 votes could give some candidate an absolute majority in the Democratic contest and 5,500 votes could make somebody an "overwhelming" victor in the Republican race.

Before the voting ever began, political analysts were explaining why the turnout would be light. They pointed out that the campaign had to be conducted in only five weeks, and five weeks is not enough time to make the public acquainted with the qualifications of 31 candidates vying for a single office.

The problem was exacerbated by the usual campaign strategy of saving a big radio-TV blitz for the final days before the election, with the result that suddenly all the candidates were on the air at the same time. Everybody said he was for reduced government spending and everybody said he was against the wholesale firing of government workers.

Before voters could resolve the question of how the candidates proposed to cut the government payroll without reducing its size, they were called upon to vote.

It is small wonder that many people feel they just can't make a choice from this vast array of politicians and political promises.

If the unusually large number of candidates confused voters, the unexplained contradictions built into those 60-second campaign speeches added to the confusion and eventually led to uninterest.

As a consequence, a small majority of voters will now be in a position to select the candidates for the 5th District seat that has in recent years been filled by an effective spokeswoman for the district's majority.

The best hope now is that two good candidates will somehow emerge from today's balloting, and that our good neighbors in Maryland will elect the better of them to Congress.

And some day we may even find a way to purge misleading promises from pre-election campaign blitzes.