It's called sucking out all the oxygen. And it's done by getting so many nominating petition signatures so early in the circulating period that there won't be too many eligible voters to sign for the opposition candidates.

As a campaign tactic, knocking a competitor off the ballot by challenging and invalidating his or her nominating petitions is a lot cheaper than having to defeat them. In this year's Chicago aldermanic elections, Northwest Side Democratic ward organizations are employing an obscure clause in the Illinois Election Code, and are seeking to politically depressurize virtually every ward, eliminating all challengers to the incumbent or slated candidate.

The statute in question, as amplified by a 1984 legal ruling, allows, upon a nominating petition challenge, the invalidation of any voter's signature who signed for more than one candidate, with the signature earliest in time taking precedence over the later. Proof of time is ascertained by examining the circulator's affidavit on the face of each petition sheet, which must set forth the date of circulation.

Using the 45th Ward as an example, here's how this tactic works. Alderman Pat Levar's popularity, to use a quaint expression, ain't what it used to be. He is facing credible opposition in the Feb. 25 election from police officer Mike Lappe and community activist Pete Conway. Other candidates who filed are Bruce Best, George Powers and Joe Schreiner. If both Lappe and Conway stay on the ballot, it is likely that the combined non-Levar total vote could exceed 50 percent, thereby forcing Levar into an April runoff, which he could lose. So, in mid-September, just after the legal period for circulating petitions began, an army of 45th Ward precinct captains began circulating petitions for both Mayor Richard Daley and Levar, and they accumulated in excess of 13,000 signatures for each within 4 weeks. On Dec. 9 Levar filed 786 pages of petitions; Lappe filed 54 pages, containing roughly 950 signatures, and Conway filed 85 pages, containing roughly 1,200 signatures.

It takes only 240 valid signatures to secure a ballot position, but the theory of "depressurizing" goes like this: Each ward has roughly 25,000 registered voters. Between elections, roughly 10 to 15 percent of them move away or die. New voters are always being enrolled, but their names don't appear on poll sheets until updated versions are issued by the Chicago Board of Election Commissioners, usually 90 days prior to an election. So candidates must use poll sheets from the last election during the circulation period. Another 10 to 20 percent of the registered voters either cannot be contacted or refuse to sign anything.

So that means Levar, with his 13,000 signatures, shrank the eligible voter pool from which Lappe and Conway could draw signatures to about 4,000. Levar entered all his petition signatures into a database, and he is in the process of comparing his signatures against those of his foes. He would have to find more than 700 duplications on Lappe's petitions and more than 900 on Conway's to have them knocked off the ballot. If he does, he must file his objections no later than Dec. 23. If they are subjected to a challenge, either opponent would have to spend thousands of dollars on legal defense fees, and would spend weeks in limbo, not knowing whether they will be on or off the ballot.

Other Democratic ward organizations that employed the "sucking the air out" strategy were the 38th Ward, where incumbent Tom Allen filed 394 pages of signatures with an estimated 8,500 names, the 40th Ward, where Pat O'Connor filed 342 pages containing some 7,500 names, the 39th Ward, where Marge Laurino filed 243 pages with approximately 5,000 names, the 36th Ward, where Bill Banks filed 558 pages that probably contained more than 12,000 names, and the 33rd Ward, where Dick Mell filed 501 pages with something like 11,000 names. And Daley, not surprisingly, with all the local committeemen using his petitions as a door-opener to get signatures for their local alderman, filed more than 100,000 signatures -- four times the 25,000 citywide requirement.

With filing for alderman having closed on Dec. 16, here's the early outlook in Northwest Side wards other than the 45th:

41st Ward: Incumbent Brian Doherty, the City Council's only Republican, was essentially re-elected in November, when his ally, state Representative Mike McAuliffe (R-20), fought off a challenge by Democrat Bob Bugielski, who also was an incumbent. Bugielski was backed by Banks, who flooded the 41st Ward with his workers. Yet McAuliffe, whose campaign was managed by Doherty, carried the 41st Ward easily, getting 10,188 votes to Bugielski's 6,109. That's a 62.5 percent share of the vote.

Banks, along with state Representative Ralph Capparelli (D-15), the ward's Democratic committeeman, intended to back John Malatesta against Doherty, but Bugielski's pasting aborted that plan. Those who filed against Doherty are writer Gloria Jean Sykes, city worker Mike Marzullo, who has been campaigning for months, attacking Doherty for failing to provide adequate city services, police officer Wayne Dembowski and Norwood Park community activist Shari Marie Centrone.

The outlook: Doherty won 14,182-4,822 over police officer Dan Burke in 1999. He should win just as comfortably in 2003.

38th Ward: Allen was unopposed in 1999, but he faces police officer Chester Hornowski this time. Allen amassed 12,021 votes in 1999, and he got 8,498 in 1995, when he had three opponents. Allen, backed by Patty Jo Cullerton's ward organization, filed more than 8,000 petition signatures, while Hornowski filed fewer than 800. A petition challenge to Hornowski is certain.

The outlook: Even if Hornowski stays on the ballot, Allen is a heavy favorite for a third term.

36th Ward: Banks may have gotten his clock cleaned in the 41st Ward, but nobody messes with him in his ward. Banks, an alderman since 1983 and chairman of the council's Zoning Committee, produced a solid, but not quite overwhelming, 6,840-4,350 win for Bugielski in the ward over McAuliffe, with Bugielski getting 61.1 percent of the total.

Banks was unopposed in 1995, getting 12,012 votes, and in 1999, getting 13,534 votes. He filed petitions this year containing more than 12,000 names; his lone opponent, David Tirado, filed 26 pages, containing more than 450 names.

The outlook: Expect Tirado to be challenged, and expect Banks to run unopposed in February.

 47th Ward: Label this "Kelly versus Schulter, Round Two." Gene Schulter ran against Ed Kelly for ward Democratic committeeman in 2000, losing by 155 votes. Kelly has been the ward's committeeman since 1964, and he plucked Schulter from obscurity to make him alderman in 1975. Kelly calls Schulter an ingrate, plus a lot of four-letter words. Kelly is backing attorney Jack Lydon against Schulter for alderman, and Lydon filed just under 3,000 signatures, to Schulter's 12,000. Schulter won 7,677-1,684 in 1995, and he was unopposed in 1999, getting 9,374 votes.

The outlook: Expect Lydon to stay on the ballot, but the fact that Schulter was able to obtain so many signatures means that either his organization is much stronger than Kelly's or that the mayor's workers did the canvassing. Schulter should win his eighth term.

50th Ward: 29-year incumbent Berny Stone pondered retirement, but he decided to seek a ninth term in 2003. Stone got 5,676 votes (56.9 percent) in 1995, beating two foes, and he was unopposed in 1999, getting 7,445 votes. His 2003 opponents are Tom Morris, a city worker, and John Salmassi.

The outlook: Stone's West Rogers Park ward has undergone huge demographic shifts in the last decade, with immigrant influxes of Indians, Pakistanis and Russians. The Jewish vote, Stone's longtime base, has dwindled, as has the pool of eligible voters. But Stone, a close ally of the mayor, should be able to win again.

Last-day filers against Laurino were Robert Klich, a retired police officer, and Dennis Patrick Healy. Last-day filers against O'Connor were Roosevelt Akins and Rafael Chagin. The incumbent is overwhelmingly favored in each race.