By Greg Giroux, CQ Staff

This Sunday will mark exactly 100 days until Election Day on Nov. 4 — a political milestone of sorts that gave the leaders of the campaign organizations of House and Senate Democrats a pretext Wednesday to put an optimistic face on their prospects.

Charles E. Schumer of New York, the chairman of the Democratic Senatorial Campaign Committee (DSCC), and Chris Van Hollen of Maryland, the chairman of the Democratic Congressional Campaign Committee (DCCC), both said that their party was positioned to increase its numbers in November — and augment the significant gains that Democrats made two years ago in capturing legislative majorities.

“We expect to pick up a whole bunch of seats,” Schumer said of an election cycle in which the seats of 23 Republican senators, including five who are retiring, and just 12 Democratic senators are being contested.

Though Democrats now control both chambers of a Congress that most of the voting public views unfavorably, Schumer pointed to polling data that show more voters presently prefer a Democratic-run Congress to one headed by Republicans.

Schumer arranged 16 Republican-held Senate seats into three rough categories of competitiveness: five contests in which he said the Democratic candidates are ahead; six in which Democrats are “even or close”; and five that “not close yet, but they’re getting there.”

In the first category Schumer included Virginia, Colorado and New Mexico, where Republican senators are retiring, as well as New Hampshire, where Sen. John E. Sununu is trailing Democratic former Gov. Jeanne Shaheen, and Alaska, where Sen. Ted Stevens faces a stiff challenge from Democrat Mark Begich, the mayor of Anchorage. Schumer’s second grouping included Oregon, Minnesota, Mississippi, Kentucky, Maine and North Carolina. He included Kansas, Texas, Oklahoma, Nebraska and Georgia in the third category. (For details about each of these races, please consult CQ Politics’ list of Senate “Races to Watch”.

The only Democratic-defended Senate seat that appears highly competitive is Louisiana, where two-term Sen. Mary L. Landrieu is opposed by Republican state Treasurer John Kennedy.

A very strong showing by Senate Democrats this November would bring the party at or very close to a 60-seat majority that could theoretically break a Republican filibuster keeping a bill from being considered or passed. With Democrats currently in operational control of 51 seats, a filibuster-proof majority would require Democrats to make a net gain of nine Senate seats — something that no party has accomplished since 1980. Schumer said a 60-Democrat Senate in 2009 was “very unlikely” but not out of the question.

Schumer said that Obama heading the Democratic ticket was a “real advantage” to his Senate campaign operation because Obama is running well in states that the DSCC is targeting. Obama “polls better than a traditional Democrat does in very [Republican-leaning] red states.”

Senate Republican campaign strategists have acknowledged a difficult political environment for their party but said some races have trended their way in recent weeks — including the contest in Minnesota, where recent missteps by Democratic nominee Al Franken have enabled Republican Sen. Norm Coleman to regain his footing.

“A hundred days is a lifetime in politics. A lot can happen, and we feel good about where our races are at this point,” said Rebecca Fisher, the communications director for the National Republican Senatorial Committee.

Van Hollen, Schumer’s House counterpart, expressed confidence that Democrats next year will control more than the 236 House seats they presently hold. Van Hollen said that there are about 75 House districts “in play,” of which 25 are being defended by Democrats and 40 to 50 by Republicans — a partisan ratio that might not have been expected after a 2006 campaign year in which Democrats thrived and after which they might have expected to defend the lion’s share of competitive districts. The DCCC, which is much better-funded than the National Republican Congressional Committee (NRCC), already has reserved $53 million in air time in 51 congressional districts.

“I do think that the big story is that we continue to be on offense, and the Republicans have not been able to take advantage of going after some of our members who might naturally have been on their radar screen,” Van Hollen said.