SCENARIOS: Senate races will determine Democratic clout

(Reuters) - With the economic crisis hurting Republicans in the elections on Tuesday, Democrats have a plausible shot to grab a 60-seat super majority in the 100-seat U.S. Senate for the first time in three decades.

To reach 60 seats, which would give Democrats the muscle to pass legislation despite any Republican procedural hurdles, they need to gain nine seats. Overall, 35 Senate seats are up for election -- 23 now held by Republicans, 12 by Democrats.

On the other side of the U.S. Capitol, Democrats are expected to pick up as many as 30 or more seats in the House of Representatives, which they now control 235-199. All the 435 House seats are up for election

Here's a look at notable Senate and House races:

* Senate Republican Leader Mitch McConnell of Kentucky. Just weeks ago, McConnell seemed headed toward an easy victory in his bid for a fifth, six-year term. Although still leading, he is now in a competitive race against Democratic challenger Bruce Lunsford, a businessman.

* Republican Sen. Elizabeth Dole of North Carolina. In seeking a second term, Dole's opponent is Democrat Kay Hagan, a state senator.

* Republican Sen. Ted Stevens of Alaska. The longest-serving Senate Republican ever, Stevens was convicted on October 27 of political corruption. He is pushing ahead in his bid for an eighth term against Anchorage Mayor Mark Begich, a Democrat.

* Republican Sen. Norm Coleman of Minnesota. He is opposed for a second term by Democrat Al Franken, a former star of the TV comedy show "Saturday Night Live."

* Republican Sen. Saxby Chambliss of Georgia. His bid for a second term is being challenged by former state Sen. Jim Martin, a Democrat.

* Sen. Mary Landrieu of Louisiana is the only Senate Democrat in a competitive race for re-election. Her Republican foe is state Treasurer John Kennedy.

* One of the most interesting House races involves Rep. Chris Shays of Connecticut. Shays, a moderate, is the only remaining House Republican from New England. He is being challenged by Democrat Jim Himes, a former Wall Street executive.

* Rep. Nick Lampson of Texas is considered among the most vulnerable House Democrats. He represents a heavily Republican district where former House Republican Leader Tom DeLay once reigned. Lampson is challenged by Republican Pete Olson, a retired Navy pilot and former congressional staffer.

(Reporting by Thomas Ferraro; editing by David Alexander and Jackie Frank)