WASHINGTON - For all the primaries testing tea party clout and veteran senators' ability to survive, a special House election in southwestern Pennsylvania is the multimillion-dollar battleground of choice Tuesday for the two political parties, previewing themes for a fall campaign shadowed by recession and voter discontent.

Competing economic prescriptions, the appeal of President Barack Obama's health care legislation, the Republicans' ability to woo crossover support from independents and Democrats all are at issue, according to officials in both parties, in a race that also features a struggle for the political high ground as Washington outsider.

The House race features Republican Tim Burns against Democrat Mark Critz to fill out the final few months in the term of the late Democratic Rep. John Murtha. But the two national parties made it something more than that when they decided several weeks ago to invest heavily - roughly $1 million apiece independent of their candidates.

"This is the kind of district that the Republicans have to win if their hype is to even begin to meet the reality on the ground," said Maryland Rep. Chris Van Hollen, the head of the Democratic Congressional Campaign Committee. He was poking at GOP boasts that the party will win the 40 seats this fall that it needs to take power in the House.

"This is the fall. This is where it happens," said Rep. Pete Sessions of Texas, chairman of the National Republican Congressional Committee.

The district is home to more registered Democrats than Republicans. There is a solid blue collar vote, the result of the area's location in the nation's coal belt, and opposition to gun control and abortion is strong within both parties. The district supported Sen. John McCain in the 2008 presidential election after siding with Democrats in the previous two races for the White House.

Private polling shows Obama's approval rating in the congressional district in the range of 35 to 40 percent, lower than it is nationally. And while the Republican Party-paid television ads and mass mailings attack his agenda, they have focused even more criticism on House Speaker Nancy Pelosi.

The Republican Congressional Campaign's sum-up television ad, airing in the final days of the race, touches on points the GOP says it intends to stress in the fall. It says the health care overhaul that passed was disastrous and will cut $500 billion from Medicare, that the House-passed energy bill is a "cap and trade scheme" that will cost jobs, that Democratic liberals voted for runaway spending and that the "Obama-Pelosi agenda only makes things worse."

As the TV image of Obama and Pelosi together gives way to one of the speaker standing alone, the announcer says, "Pennsylvania can send Nancy Pelosi a message. Or send her Mark Critz."

Democrats have hit back hard on pocketbook issues, including jobs, as they seek to avoid a backlash from voters angry over a steady loss of jobs that has only lately showed signs of abating.

"Southwestern Pennsylvania is hurting, but millionaire Tim Burns would make things worse," says one ad aired by the Democratic Congressional Campaign Committee. Referring to a proposed value added tax, it goes on, "Burns supports putting a 23 percent national sales tax on just about everything we buy," groceries, gas and medicine included. "We can't afford to pay 23 percent more. We can't afford Tim Burns."

Public polling nationwide shows Republicans are more eager to cast ballots this fall than Democrats, and surveys also indicate the GOP is attracting the independent voters whose support was essential in 2006 and 2008, when the Republicans lost control of Congress and then the White House.

But an intensely competitive Senate primary in Pennsylvania is likely to swell turnout by Democrats, and Republican strategists say Burns must appeal to them and to independents if he is to win.

The same energy that Republicans hope will power then to victory in the fall has transformed the party's senatorial primary in Kentucky into an unpredictable contest.

"I'm not running to be the candidate of the tea party," Secretary of State Trey Grayson said Monday as he closed out his race with political newcomer Rand Paul. "I'm running to be the candidate of this Republican Party of Kentucky."

Paul, the son of Rep. Ron Paul of Texas, said he'd happily accept support from both.

The race to succeed retiring GOP Sen. Jim Bunning has divided the Republicans for weeks. The Senate GOP leader, Kentucky Sen. Mitch McConnell, helped push Bunning to the sidelines and recruit Grayson. Last week, as polls showed Paul opening a substantial lead, McConnell stepped in with an endorsement of his recruit that quickly became a statewide television commercial.

In Pennsylvania, Sen. Arlen Specter switched parties a year ago and drew the support of Obama, organized labor and Pennsylvania Gov. Ed Rendell as he set out to win a sixth term, his first as a Democrat.

But Rep. Joe Sestak grabbed late momentum with a television commercial that showed his rival saying he had switched parties so he could win re-election. Late polls showed a highly competitive race.

In Arkansas, Lincoln's path to a third term ran into a primary challenge from Lt. Gov, Bill Halter, who has the support of the Service Employees International Union, which is unhappy with the incumbent's positions on health care, union organizing and more.

A pro-business group, Americans for Job Security, countered with more than $1 million for an ad that purported to "thank" Halter for helping ship jobs overseas.

Late polls showed Lincoln ahead in a multi-candidate race, but far from certain of the 50 percent threshold needed to avoid a runoff.

Primary defeats have already claimed two longtime lawmakers in recent days: Republican Sen. Bob Bennett of Utah and Democratic Rep. Alan Mollohan of West Virginia.