It's the grunt work of politics. It's unglamorous and unpublicized, but it's hardly unnecessary.

It's called canvassing, and volunteers for all three major Democratic mayoral candidates have started the [WORD ILLEGIBLE] and time-consuming effort to identify by name the 40,000 voters it likely will take to win Sept. 12 primary election.

The idea behind canvassing the city's 185,000 registered Democrats - or at least a large majority of them - as to leave nothing to chance. It is not enough in a crucial and close election the campaign strategists believe, to till the airwaves with slick advertisements extolling the virtues of their candidates for the contenders to visit every neighborhood in the city.

By pinpointing the people who are committed or leaning to one of the three candidates - Mayor Walter E. Washington. City Council Chairman Sterling Tucker and council member Marion Barry - the campaigns know where their support is and can then attempt to get their voters to the polls on election day.

But the strategists say canvassing works in the opposite way, too. If a person is supporting another candidate, that voter is largely forgotten. There's no wish to run a general get-out-the-vote campaign - except for their man. Undecided voters are also identified and they are plied with campaign issue papers and other literature in an attempt to bring them onto the list of committed voters.

"There is no romance to it," Ivanhoe Donaldson, Barry's campaign manager, said of canvassing, "It's nothing but hard work. But you got to do it."

Tucker's Ward I coordinator and a canvasser. Iris Lanham, says, "It's what I call the trenches, but I love it."

Donaldson says that the Barry campaign has been canvassing since February and so far has reached 25,000 voters, while the Tucker camp estimates it has surveyed 10,000 voters. The Washington campaign will not say how many voters it has reached so far, but the number is likely to be less than either Barry or Tucker because the mayor's volunteer workers only started canvassing three weeks ago.

While none of the campaigns would say what their canvassing tells them about their candidate's standing, all agree that a large number of voters - perhaps one-third of them - are undecided. Thus the canvassing becomes even more crucial to find not only the voters who are already committed but to find and try to sway the hearts and minds of the uncommitted.

Telephone and door-to-door canvassing generally work from lists of registered Democratic voters, but in the District that presents the first problem to reaching the would-be voters: There are no telephone numbers listed on the voter sheets and many of the voters have died, or, more likely, moved from the addresses filed with the D.C. Board of Elections and Ethics.

"There are some precincts where half the information is wrong," Donaldson said.

So campaign volunteers have been looking up thousands of telephone numbers before they can even start to canvass.

Donaldson said that 60 percent of the people canvassed by Barry's workers have been surveyed in prison. The ones who are identified as confirmed supporters are usually asked if they would like to work for the campaign or perhaps invite some people to their home to hear the candidate speak.

Barry's campaign manager said that in another month uncommitted voters will be sent Barry's platform and perhaps invited to a campaign event in their neighborhood. Some of the Barry mailings to these people are also targeted, depending on the community they live in or questions they may have asked about specific issues. Donaldson said. A homeowner living in a neighborhood with rapidly rising tax assessments, for example, might get Barry's position paper on real estate taxes.

Tucker's campaign has tried to do much of its canvassing while workers are also collecting the required 1,826 signatures to get their candidate on the ballot. The Tucker camp has put together a list of 105,000 Democratic voters who have voted in at least one of the city's last five elections and then set an arbitrary goal of canvassing 20 percent of those voters by the Fourth of July, a goal that deputy campaign manager Lee Carty said was about half met.

The canvassers mark their tally sheets with numbers one to five - one is a committed Tucker voter, a two is someone leaning to Tucker, a three is an undecided voter, a four is a supporter of another candidate and a five is a nonvoter or someone who will not voice their intention.

"We're urging our workers not to do any fudging, not to write someone down as a confirmed supporter unless they really are," Carty says. 'And not to take any spouses' word" about their husband's or wife's inclination.

"We'll keep a list of the confirmed in the office," Carty said. "They'll be getting newsletters and invitations to fund raisers."

Carty said the list of confirmed Tucker voters will be computerized and then on election day precinct workers will try to made sure that these voters get to the polls.

Although some canvassing has been done in previous elections in the city, it apparently has not been done on the scale it is in this year's mayoral campaign, the second since Congress granted the District limited home rule.

"This is essentially the first big city election in the District," Carty said. "It's a new kind of politics."

Both Barry and Tucker have themselves been doing some of the canvassing, hiking door to door to make their pitches on why they would make a good mayor. But it is a time-consuming task for more than one reason, Carty said.

"You always have to schedule some shower time after those walks," she said. "Running up doorsteps is hard work."