The 2012 Senate battleground is pretty much set one year before voters go to the polls, but the parties’ spending strategies are evolving in uncharted territory.

With an unprecedented level of spending from the presidential campaigns and outside groups expected next fall, the Senate campaign committees are preparing to adjust how they spend their limited resources in the fight for 51 seats.

Media strategists see 2012 as a revolutionary year for political advertising, with the market share for online video — currently  in the low single digits — expected to double or triple. The increase in Americans watching TV shows and videos online has created an inventory for new opportunities to purchase pre-roll and in-stream space that simply wasn’t available in 2008.

“If you’re in one of these battleground states, it’s going to be a lot more complicated to get your message out,” said Eli Kaplan, a Democratic online media strategist at Rising Tide Interactive. “There’s only so many gross ratings points to go around.”

The Democratic Senatorial Campaign Committee and National Republican Senatorial Committee will have plenty of company on the airwaves in states competitive at the presidential level, with the presidential campaigns combined with top labor unions, the U.S. Chamber of Commerce and a growing number of super PACs.

Erik Potholm, a GOP strategist at SRCP Media, said both price and placement will be challenges for campaigns in 2012. “Your opponent could be on ‘60 Minutes,’ while your campaign gets stuck with a low-rated alternative like ‘A Gifted Man,’” he said.

“Two words of advice for the 2012 fall campaign,” Potholm said. “Place early.”

States such as Florida and Ohio will be crawling with presidential and national party committee field programs, and the airwaves will be flooded for at least the last eight weeks of the campaign, resulting in air space and prices at a premium. That could entice national Republicans and Democrats to go on the air earlier or shift a portion of their ad resources to a different medium.

In flyover territory for President Barack Obama and the GOP presidential nominee, where the Senate race will be the biggest statewide contest, the committees will have clearer airwaves but will need to invest more resources in their ground games. The Obama campaign actually has an organization in all 50 states, though some are more robust than others. The president won’t be seen much in Montana or Nebraska, states that aren’t part of his calculus to get to 270 electoral votes. But both states are vital to control of the Senate, as are Virginia and Nevada, where the president will be actively campaigning.

Beyond the positive or negative downballot effect Obama brings for Democratic incumbents, this dichotomy within the Senate battleground will have strategic ramifications for campaign committees, outside groups and the candidates.

States with varying degrees of competition at both the presidential and Senate levels include Florida, Michigan, Nevada, New Mexico, Ohio, Virginia and Wisconsin, with Democrats playing defense in all but Nevada.

Top Senate battlegrounds not expected to be as competitive at the presidential level are Hawaii, Massachusetts, Missouri, Montana and Nebraska, with Democrats defending all but Massachusetts. Missouri was the only state heavily targeted by Obama in 2008 that he did not win.

Democrats are hoping to move three more states onto the Senate battleground map: North Dakota, Indiana and Arizona. Obama won Indiana in 2008 and his campaign sees an opportunity in Arizona this time, but North Dakota is a nonstarter for the president and the open Senate seat will be the Democrats’ toughest hold. Roll Call rates the race Safe Republican.

The Senate is up for grabs, with Democrats holding a surmountable 53-47 majority. There are eight races that Roll Call currently rates as tossups. Winning North Dakota, Nebraska, Montana and Missouri would be enough for Republicans to secure the majority, but the party will also need to defend Massachusetts and Nevada.

DSCC Executive Director Guy Cecil cited the committee’s “unprecedented early investment in research and communications infrastructure in more than a dozen key states” and an expanded in-house research operation that includes some 21 trackers, “all to be able to define the Republicans as early as possible.”

“In addition to funding aggressive television buys, we will invest heavily in field operations in many states, particularly in races where the presidential will be less of a factor,” Cecil said.

Obama’s ground game is well-documented and an obvious bonus for Democrats running in the states where his grass-roots operations are strongest. Republicans in competitive presidential states can also count on support from the eventual GOP nominee and the Republican National Committee, which was not much help last cycle to the other GOP committees.

NRSC Executive Director Rob Jesmer wouldn’t offer details but said his committee will also invest in field operations, tracking and communication efforts in states where the presidential contest won’t be competitive. He sees a distinct advantage for Republicans in those states, reasoning that voters  there won’t vote for a Senator who supported Obama’s legislative priorities.

But Democrats believe they can more easily make the races in those states a choice between two candidates — localize rather than nationalize. Senate races generally don’t follow the national mood as much as presidential and even House races do.

Jesmer said early spending by Republican outside groups in 2010 was helpful and that such organizations can help frame a race, though the campaign committees are prohibited by law from working with third-party groups.

“It gave us some flexibility late,” Jesmer said. “We need to be more flexible, in a way, than they do because we are a party committee. Things pop up, incumbents pop up, so we need to have flexibility at the end in spending.”

The American Crossroads super PAC, combined with its issue advocacy arm Crossroads GPS, raised $71 million in the 2010 cycle. The Crossroads groups are expected to raise and spend $240 million in the 2012 cycle, which will include spending at least another $71 million on House and Senate races, spokesman Jonathan Collegio said.

Collegio agreed that with the focus on the presidential contest, “The committees and outside groups are going to have to make extra calculated decisions as to where to invest their resources, and in many cases those expenditures are going to come earlier.”

Correction: Nov. 14, 2011

The ratings map originally transposed the ratings for New Hampshire and Vermont.