An avalanche of money, some of it untraceable by the public, is set to flow into political television advertising as Republicans and Democrats battle for control of both houses of Congress.

The last-minute injection of funds, just weeks before the election, is expected to come through free-standing political groups that are required to operate at arm’s length from individual campaigns and the political parties.

“I think you’re going to see an explosion of activity,” a veteran Republican political consultant, Scott Reed, said yesterday. “There’s a lot of pent-up money right now in the system.”

One group at the forefront of the pro-Republican effort is Progress for America. The organization was founded in 2001 but emerged in 2004 as the leading independent committee on the right, taking in almost $45 million for advertising supporting President Bush and attacking his Democratic opponent, Senator Kerry of Massachusetts.

One person familiar with Progress for America’s operation said yesterday that, as of last month, the group had amassed between $35 million and $40 million from conservative donors. A spokeswoman for the organization, Nicole Philbin, declined to release fund-raising numbers.

Democrats have no independent group on that scale, but a top Democratic organizer, Harold Ickes, is raising money for an organization called the September Fund, which will try to match the Republicans.

A firm that tracks political advertising, TNS/Media Intelligence, said Progress for America has spent about $3 million so far this season. Its new advertising emphasizes the threat posed by terrorism and the connection to the war in Iraq. To deliver its message, the group has signed up a compelling spokesman, David Beamer, whose son, Todd, led the charge against the hijackers of United Airlines flight 93 on September 11, 2001.

“Todd and United 93 fought back on 9/11. We continue this fight in Iraq today,” Mr. Beamer declares in the group’s latest television spot. “This enemy must be destroyed, in Iraq, and wherever we find them. There can be no retreat in this war.”

The ads are running in Missouri and Ohio, as well as on some national cable networks. Progress for America said it also has purchased “tens of thousands” of DVD copies of a film, “United 93,” that depicts the response of passengers on that plane, which crashed in Shanksville, Pa., but is believed to have been part of an attempt to attack the Capitol or the White House. Hundreds of thousands of e-mails, with a message from Mr. Beamer, have been sent to residents of Missouri and Ohio, urging them to accept a free DVD and hold a viewing for their neighbors.

An earlier Progress for America ad echoed a Republican talking point recently adopted by Mr. Bush, claiming that Democrats want to “cut and run” in Iraq.

A professor of political science at St. Louis University, Kenneth Warren, called the ads “very effective.”

“It’s more of what Karl Rove promised,” Mr. Warren said. “It’s definitely going to help Republican candidates.”

“What they’re doing right now is kind of interesting and kind of groundbreaking,” an analyst with TNS/Media Intelligence, Evan Tracey, said. He said Republican candidates would take flack from the press for trying to whitewash the problems in Iraq, but the group faces no real consequences. “Progress for America is not on the ballot,” Mr. Tracey noted.

While Progress for America’s ads in 2004 directly praised Mr. Bush and savaged Mr. Kerry, the group’s spots this year make no reference to any candidate. While Mr. Beamer urges those receiving the DVD to “take action,” neither the TV ads nor a related Web site make any mention of the election.

Mr. Warren said the failure to mention the election or any candidates reduces the electoral impact of the ads. “It’s more implicit,” he said. “A lot of people who don’t pay much attention to politics, they won’t make the connection.”

The reasons for the change in tactics are not entirely clear. While the bulk of the money collected by Progress for America in 2004 went into a so-called 527 group, the spending this year is coming from a different account, known as a 501(c)(4). Both designations come from sections of the tax code.

The 527 groups can mention candidates in TV or radio ads, but those organizations also have to disclose the names of donors and the amounts received. The 501(c)(4) groups cannot mention candidates in pre-election broadcast or cable ads, but are under no obligation to make public any information about their donors. As a result, gifts to Progress for America’s current ad campaign are essentially untraceable, and the group’s fund-raising totals may not become public for a year or more.

A report filed yesterday by Progress for America’s 527 shows limited fundraising activity by that branch through September of this year. A California investor who made his fortune at the helm of Univision, A. Jerrold Perenchio, gave $1 million. The CEO of Public Storage Inc., B. Wayne Hughes Sr., gave $500,000. Major backers of the group in 2004 included a developer who owns the San Diego Chargers, Alexander Spanos, who gave $5 million, and an heir to the Wal-Mart fortune, Alice Walton, who gave $2.6 million.

Progress for America’s inner workings are murky. In a 2002 interview with the Washington Post, an ambassador to the United Nations under President Reagan, Kenneth Adelman, described himself as the chairman of Progress for America. Reached by the Sun this week, he confirmed his ongoing involvement with the group but declined to elaborate. “I’m not interested in chatting about it,” he said.

The group’s spokeswoman, Ms. Philbin, declined to identify its principals or to explain the switch this year to the 501(c)(4).

Some of the secrecy is aimed at giving Democrats little intelligence about the conservative group’s battle plan, but the reticence could also stem from the fact that the Federal Election Commission has ongoing investigations into a number of prominent 527 groups. There is also evidence that Progress for America may be under close scrutiny. It has run up hefty legal bills, paying more than $750,000 this year to an elite Washington law firm, Patton Boggs LLP.

A lawyer there, Benjamin Ginsberg, wrote to the FEC last month, complaining that legal uncertainty surrounding the groups is “dampening fund-raising.”

Progress for America’s fund-raising and ad buying is run by employees of a Republican political consulting firm, DCI Group, which also helped run another anti-Kerry organization, Swift Boat Veterans for Truth. DCI’s chairman, Thomas Synhorst, worked as a political aide to a former Senate majority leader, Bob Dole, and is credited with Mr. Dole’s upset win in the Republican presidential caucuses in Iowa in 1988.

Some Democrats refer to DCI as “Karl Rove central.” A political marketing firm with close ties to DCI, FLS Connect, features on its Web page an endorsement from Mr. Rove. “I know these guys well,” the site quotes the top White House political adviser as saying, “They work as hard to win your races as you do.”

A spokeswoman for Mr. Rove, Tracey Schmitt, said any suggestion he is involved with any 527 group is “patently false.”

DCI Group is a regular landing spot for Republican Party loyalists. The firm has employed some people other GOP firms might have turned away, such as a former Northeast regional political director for the Republican National Committee, James Tobin.

Tobin took a job at DCI Group while under investigation for involvement in a scheme involving jamming of Democratic get-out-the-vote phone banks in New Hampshire during the 2002 election. Last year, he was convicted on two felony charges relating to the case and sentenced to 10 months in prison. Tobin is free pending appeal, but a DCI employee said yesterday that he is no longer working for the firm.

According to an FBI report, a GOP official who served a seven-month sentence for the phone jamming, Charles McGee, said he ran his plan by a DCI Group employee who now serves as Progress for America’s president, Brian McCabe. McGee told federal prosecutors that Mr. McCabe “stated he had never heard of an idea such as this,” the FBI memo says.

Mr. McCabe, who was not available for an interview for this article, was not charged in connection with the voter-suppression scheme.