In a sign that 2010 could be the most expensive election cycle on record for incumbent Senators, more than half of the 34 Republicans and Democrats facing re-election already have amassed war chests of at least $1 million –– and some are sitting on treasure troves of cash.

A survey of the most recent Federal Election Commission filings available through March 31 shows that at least eight of the Democrats and 10 of the Republicans in line for another term next cycle are minding seven-figure bank accounts. Of those, at least two Democrats –– Sens. Evan Bayh (Ind.), a one-time 2008 presidential hopeful, and Charles Schumer (N.Y.), the Democratic Senatorial Campaign Committee chairman –– and one Republican, Sen. Richard Shelby (Ala.), have at least $10 million in their coffers.

Senators and aides said the rush to raise money eight months before the 2010 cycle officially begins is no surprise given the competitive political landscape and the expense associated with a typical campaign these days. The move comes on the heels of a 2006 cycle that swept the Democrats to power with the defeat of six GOP incumbents.

“There’s a recognition from incumbent Senators that the world has changed,” said a Democratic strategist who works on Senate campaigns. “You need more resources than ever.”

“A lot of elections are won and lost before the filing deadline,” said Sen. John Thune (R-S.D.), who has $3.3 million on hand for 2010 and pulled in $387,000 in the first three months of this year. “The most obvious commitment you can make to a race is to get out there and start hustling early.”

Representing a GOP-leaning, conservative state, Thune is among incumbent Republicans who probably will have a comfortable ride to re-election in 2010. But he and, others in similar positions –– such as Shelby –– are not taking chances. Shelby won his last re-election with 68 percent of the vote.

“I am making sure I am heavily armed and able to compete,” said Shelby, who is sitting on a whopping $12.8 million. “But you never know in today’s atmosphere.”

In addition to Thune and Shelby, other GOP Senators have joined the million-dollar club, including Sens. Kit Bond (Mo.) with $1.3 million, Mike Crapo (Idaho) with $1.7 million, Jim DeMint (S.C.) with $1.1 million, Chuck Grassley (Iowa) with $2.6 million, Johnny Isakson (Ga.) with $2 million, Mel Martinez (Fla.) with $1.3 million, Arlen Specter (Pa.) with $4.6 million and George Voinovich (Ohio) with $2.1 million.

Voinovich, Bond, Martinez, Specter and Grassley are likely to be among the top Democratic targets next cycle. That prospect could be one of the reasons why Specter and Grassley in particular announced their re-election plans more than a year ago –– some two years ahead of the official start of the 2010 cycle.

Grassley has been a consistent vote-getter, and he’s believed to be less vulnerable than Specter, who, as a moderate, faced a challenge from the right in 2004 and could see both a primary and general election fight next cycle. In the Republican money chase, Specter is second only to Shelby, with $4.6 million in the bank, having brought in $814,000 in the first three months of this year –– the largest quarterly amount for any 2010 incumbent.

A GOP strategist who works on Senate races said the 2006 election –– which sent Congressional Republicans into the minority –– served as a wake-up call, underscoring that no Senator –– no matter how popular –– is safe.

“It was an eye-opener,” the operative said. “I assume the same is true for the Democrats, but certainly it is for Republicans. You can’t just walk into a seat anymore. For the first time, many Senators are running in really tough races. It’s very telling, and a lot of these guys need to start early.”

Republicans are feeling the pressure after last cycle’s results and in the face of 2008, where 23 GOP seats are up for grabs, compared with just a dozen Democratic ones. The playing field is a little more even in 2010, but Republicans still must defend 19 seats and Democrats 15.

Still, not every incumbent next cycle seems to be worried. Sen. Tom Coburn (R-Okla.) has just $73,000 on hand, the lowest of any 2010 incumbent. On the Democratic side, Sen. Chris Dodd (Conn.) –– fresh off an unsuccessful presidential campaign –– is bringing up the rear with just $89,000 in the bank.

On the flip side, the wealthiest Democratic incumbents in 2010 include Majority Leader Harry Reid (Nev.) with $2.4 million and Sens. Ken Salazar (Colo.) with $1.5 million, Byron Dorgan (N.D.) with $1.3 million, Patrick Leahy (Vt.) with $1.2 million and Daniel Inouye (Hawaii) with $1.1 million.

While most of those Democrats should be safe next cycle, Reid and Salazar are likely to be among the GOP’s top 2010 targets. Republicans also are likely to keep an eye on a possible open seat left by presidential aspirant, Sen. Barack Obama (Ill.), and the seat now held by Sen. Blanche Lincoln (Ark.), who hails from a conservative- leaning state and who, so far, has just $425,000 in her account.

The Democratic strategist reminded that the “best way to avoid having a challenger when you are in cycle is to raise money when you are out of cycle. The best way to do it is to go in with a healthy amount in the bank.”

Seeming to follow that advice, Salazar, a first-term incumbent who represents the swing state of Colorado, said Tuesday that while he hasn’t gone through a re-election race before, he’s “working hard at it” and is doing what’s necessary to be prepared for another bid. Salazar faced a grueling campaign against beer magnate Pete Coors in 2004.

“I’ve never taken anything for granted in my political life,” Salazar said.