By Bob Benenson, CQ Staff

The Democrats are maintaining their momentum from the 2006 midterm elections, when big gains gave the party control of both chambers of Congress. And, the success of Democratic strategists at putting dozens more Republican seats “in play” this year has made it likely that they will significantly expand majorities in both the Senate and the House.

Using the same method that has worked well for CQ’s election analysts over decades, we’ve been tracking 481 Senate, House and governorship races for two years and have deemed an unusually high figure of 135 races as at least somewhat competitive.

On Tuesday, we at CQ Politics find out how well we did with our ratings.

But first, my own personal estimates. I predict that Democrats are likely to gain eight Senate seats and in the neighborhood of 25 House seats. With only a small handful of the 11 governors’ races highly competitive, I foresee a net gain of one for the Democrats.

These predictions are made with more trepidation than bravado, because they are predicated on this major intangible: that the Democrats, as the party that appears be on a roll heading into Election Day, will win the three of the four open Senate races (all for Republican seats) and many of the 26 House races (20 for Republican seats) that we currently have in our No Clear Favorite, or tossup, category. That has been the pattern for the party on the ascendancy in most recent election cycles.

Second, one last explanation of what these ratings mean.

The most important point to remember is that any race that is not rated Safe Democratic or Safe Republican is at least somewhat competitive. The No Clear Favorite category is self-defining: It means those races could go either way. But those races rated Leans Democratic and Leans Republican also are regarded by our analysts as highly competitive, and while the candidate of the named party has at least a slight edge, it would not be a shock to see the other party win that contest. And even those races rated Democrat Favored or Republican Favored — meaning the named party is likely to win — carry the warning label that an upset is not an unrealistic possibility.

In just about every election cycle, upsets do occur. We’ll kick ourselves — and undoubtedly we’ll get some outside heckling, too — if a race rated Republican Favored goes Democratic or vice versa. But we can say, at least, that we put these contests on the map for our readers.

That is, unless one of those candidates rated as “safe,” defined as “we don’t see any way that this candidate can lose,” goes down in the upset of the year. In the last six election cycles, we have not blown a “safe” call, and we believe we’ve done everything we can to extend that winning streak. We’ve “sanitized” the Safe columns of all races in which we believe there is a realistic chance of an upset — without making unnecessary moves just to cover our keisters.

Please check back with CQ Politics through Election Day, as it is more likely than not that there will be some last-minute rating changes based on developments in the campaigns. But for now, here’s how those Balance of Power scorecards stand.

• Senate. CQ Politics currently rates the Democrats as slight to heavy favorite in races for six seats currently held by Republicans. One of those, in Virginia, looks like a lock for the Democrats. Two others, in New Mexico and Colorado, now appear highly likely to turn Democratic.

The other three, in New Hampshire, Alaska and North Carolina, appear closer coming down to the wire, but the Republicans’ chances of holding the latter two seats were hit hard by bad publicity last week. In Alaska, long-serving Republican Ted Stevens was convicted in federal court in Washington, D.C., on seven felony counts of failing to report lavish gifts from business interests in his home state, and polls showed a significant bump in favor of his Democratic opponent, Anchorage Mayor Mark Begich. In North Carolina, Republican Sen. Elizabeth Dole ’s campaign ran a pair of corrosively negative TV ads against the Democratic challenger, state Sen. Kay Hagan, that attempted to tie the former Sunday School teacher to an organization of atheists because a fundraiser staged in her honor was co-hosted by two members of that group; the result was a backlash that brought Dole condemnation from most of the major newspapers in North Carolina.

Democratic opportunities extend to the No Clear Favorite category, made up of races for Republican seats in Minnesota, Oregon and Georgia. And there are three races, in Kentucky, Maine and Mississippi, in the Leans Republican category to just one, in Louisiana, that is rated Leans Democratic.