AUGUSTA — The five-way Democratic primary contest in Maine’s 1st Congressional District opened as something of a sprint to begin with, when incumbent Joseph E. Brennan took until almost New Year’s to decide to vacate the post to run for governor.

The candidates are up and running now. And, with the primary voting just seven weeks away, it looks like it will take a sustained stretch drive by upset-seeking Thomas H. Andrews, dark horse Elizabeth H. Mitchell or long shot Linda E. Abromson to overtake original front-runner James E. Tierney.

The fifth candidate, Ralph Conant, appears to have fallen off the pace, although with a large field and an electorate of unknown proportions few things can be held certain for now.

What is known is that Tierney, the attorney general who was defeated in a bid for governor four years ago, continues to promote himself as the betting favorite in the field, apparently hoping to pre-empt any momentum swing that could fuel a late charge by one of his rivals.

Such has been Tierney’s strategy since the earliest days of the campaign, when he released copies of a poll he commissioned that gave him a wide lead over the rest of the field.

Andrews, Mitchell and the others grudgingly concede that Tierney, by virtue of his highly visible attorney general’s post and exposure during the 1986 gubernatorial campaign, entered the race with the most recognizable identity.

But they are counting on Tierney’s reputation to include some negatives, and are laying plans to boost their own visibility in hopes of passing him in the only poll that counts — the June 12 primary election.

Mitchell, the unsuccessful Democratic candidate for U.S. Senate in 1984, has since February mounted a modest but steady series of brief television spots aimed at restoring her identity among potential voters.

Andrews, a state senator from Portland, will probably also have to take to the airwaves heavily to augment his vaunted grass-roots organizing effort.

Last week, he called his first-quarter fund raising, which amounted to about $65,000 and bested Tierney by a narrow margin nearly equal to his own $5,000 contribution, a pleasant but only partial step toward a pre-primary goal of between $150,000 and $200,000.

How all the late broadcast advertising affects voter turnout may be the key to the outcome.

Tierney, long in the top rank of the party’s up-and-comers, is now a familiar if no longer fresh face and is watching many of the most active Democratic operatives gravitate toward Andrews.

Andrews is also the beneficiary of an outbreak of peace among some of the Democratic factions within his home city of Portland. There, adversaries from Andrews’ heated primary battle with Gerard P. Conley Jr. for the state Senate seat vacated by Conley’s father in 1984 are treating Andrews’ congressional candidacy as an opportunity to bury the hatchet.