Susan Walsh, Associated Press
Republican presidential candidate, Rep. Michele Bachmann, R-Minn. takes part in a news conference on Capitol Hill in Washington, Wednesday, July 13, 2011.

DES MOINES, Iowa — Republican presidential hopefuls have been slow to begin their television ad war but the biggest onslaught is about to begin.

Tim Pawlenty has reserved an estimated $200,000 of network television advertising in the Des Moines media market, according to information provided to The Associated Press by Republican media trackers.

The bloc of ad time for the former Minnesota governor represents the biggest of the 2012 campaign by any candidate in any state. Pawlenty has said his campaign needs to demonstrate momentum at the straw poll, a test of campaign support in the leadoff caucus state.

The ad time is scheduled to begin Monday and run through the Iowa Republican Party straw poll on Aug. 13.

Despite more than a year and a half of networking in his neighboring state of Iowa, polls show support for Pawlenty in the single digits. Earlier in the year he said he would need to "win or do very well" in the February caucuses, he has recently tried to lower those expectations.

The ad buy represents a substantial wager for Pawlenty, who reported Friday that he had $1.4 million to spend on the 2012 primary campaign at the end of June. Pawlenty, who this month became the first to begin airing candidate ads, is on pace to have spent more than $430,000 on advertising in Iowa through mid-August.

By this time four years ago, Mitt Romney had spent roughly $1.5 million on television advertising in Iowa. Romney, little-known nationally in early 2007, began advertising in Iowa in February that year. He went on to win the August straw poll and finish second in the caucuses the following January.

Romney, who is again seeking the GOP nomination, is putting far less emphasis on Iowa this time. For now, he is focusing more on New Hampshire, home of the first-in-the-nation primary.

But in early media buys, the presidential field has largely ignored New Hampshire voters.

GOP candidates have so far invested just $54,000 in the first-in-the-nation primary state; Texas Rep. Ron Paul accounts for $44,000 of that. Meanwhile, the Republican field has spent almost $690,000 in Iowa.

Pawlenty became the first candidate to air campaign ads on Iowa television with a late June spot introducing himself. Last week, his campaign launched a new ad where he discusses his record in Minnesota.

Pawlenty aides said they expect to introduce new ads in the coming weeks but declined to discuss their themes.

While Pawlenty has spent more than any of his rivals, the entire field has spent less than $750,000 on television and radio advertising time, far less than Republican candidates had at this point in the 2008 race.

Romney has spent nothing on television advertising to date, despite having ended the quarter with $12.6 million on hand, vastly more than any of his rivals.

Paul is second in advertising spending at $167,000, and Minnesota Rep. Michele Bachmann has spent $120,000. Former Pennsylvania Sen. Rick Santorum is last with $19,000 spent on advertising.