By JIM RUTENBERG — The New York Times.

OVIEDO, Fla. — The anonymously financed conservative groups that have played such a crucial role this campaign year are starting a carefully coordinated final push to deliver control of Congress to Republicans, shifting money among some 80 House races they are monitoring day by day.

Officials involved in the effort over the midterm elections’ final week say it is being spearheaded by a core subset of the largest outside conservative groups, which have millions of dollars left to spend on television advertisements, mailings and phone calls for five potentially decisive Senate races, as well as the scores of House races.

Bolstered by a surge in last-minute donations and other financial support, outside liberal groups and unions say they are stepping up their response in advertising and get-out-the-vote efforts, but remain largely outgunned by the scale and sophistication of the operation supporting Republican candidates.

A vivid picture of how outside groups are helping Republicans across the country can be found here in central Florida. The incumbent Democrat, Representative Suzanne M. Kosmas, had a nearly four-to-one fund-raising advantage over her Republican challenger, State Representative Sandy Adams, at the end of September.

Ms. Adams, low on cash, has not run a single campaign commercial. But a host of outside groups have swept in to swamp Ms. Kosmas with attack ads, helping establish Ms. Adams as the favorite without her having to spend on television.

Many of the conservative groups say they have been trading information through weekly strategy sessions and regular conference calls. They have divided up races to avoid duplication, the groups say, and to ensure that their money is spread around to put Democrats on the defensive in as many districts and states as possible — and, more important, lock in whatever gains they have delivered for the Republicans so far.

“We carpet-bombed for two months in 82 races, now it’s sniper time,” said Rob Collins, president of American Action Network, which is one of the leading Republican groups this campaign season and whose chief executive is Norm Coleman, the former senator from Minnesota. “You’re looking at the battle field and saying, ‘Where can we marginally push — where can we close a few places out?’ ”

Democrats said the conservative groups were upending some of their best-laid plans in several important races, like here in Florida, especially those in which they had been counting on the financial advantages their candidates had over lesser-financed Republicans at the beginning of the general election.

Filings with the Federal Election Commission over the weekend show that one Republican group, American Future Fund, has purchased more television advertisements attacking Representative Bruce Braley, Democrat of Iowa, who was expecting an easier path to re-election. Another group, the 60 Plus Association, reported spending more than $150,000 against Representative Solomon P. Ortiz, Democrat of Texas, who has been considered a likely victor in November against his cash-short challenger, Blake Farenthold.

“As you know, they have been dumping tens of millions of dollars of secret money into these campaigns,” Representative Chris Van Hollen of Maryland, the chairman of the Democratic Congressional Campaign Committee, said in an interview. “I would say the outside groups have shuffled the deck in a number of these races.”

The coordinating effort is led out of a nondescript office suite just blocks from the White House, where two groups formed with help from Karl Rove — American Crossroads and Crossroads GPS — share space with American Action Network, a nonprofit advocacy group. Together those strategists had already committed nearly $45 million for advertisements among them, according to Democratic advertising monitors’ best estimates. That does not include millions more being spent to get voters to polls through mailings, phone calls and text messages.

Their office suite — which has been deluged with incoming messages from nervous donors asking for progress reports or offering advice — is also the site of the weekly strategy sessions, which have up to roughly 25 representatives from other Republican groups active this campaign season, participants say.

A secondary hub is in Alexandria, Va., at the office of the Crossroads groups’ political director, Carl Forti, a protégé of Mr. Rove’s whose company does communications consulting for Americans for Jobs Security and the 60 Plus Association, which have spent more than $12 million between them this election cycle.

Working from color-coded master spreadsheets — one of which was obtained by The New York Times — the conservative groups are now closely monitoring polling in 80 House races that they judge crucial to ensuring a Republican majority. Based on those results, the groups have started to place their final advertising bets in ways carefully coordinated to fill openings left by the more financially limited official party and candidate committees.

In several cases, officials with the outside groups said, they intend to force Democrats to spend money in districts they presumed safe; in others, they said they would wipe out financial advantages Democratic incumbents were counting on to stave off strong challenges from underfinanced opponents.

“We’re going to continue to have a very strong presence on the Senate and in each of the key House races where we’ve played a big role,” said Steven Law, the president of American Crossroads and Crossroads GPS.

The groups, he said, are planning “an expansion of that effort, where we see holes and gaps.”

Over all, they said, their moves are most acutely focused on those races determined to be the most critical in securing Republican Congressional control, rather than on tantalizing but long-shot attempts to defeat Democratic nemeses like Representative Barney Frank of Massachusetts.

Both sides reported seeing an influx of new spending by liberal outside groups that had generally been subdued until now — a late-stage cavalry effect that Mr. Law called “alarming from my vantage point,” though he wondered if it was coming a bit late.

A group called Women’s Voices Women Vote recently began a significant advertising campaign against Ken Buck in Colorado, the Republican challenger to Senator Michael Bennet; Commonsense Ten, a liberal group that had been mostly focused on Senate races, has started a new advertising campaign to help Mr. Braley of Iowa.

“It’s clear that both institutional donors and individual donors dug deep over the last two or three weeks, and it will make a difference for sure,” said Jim Jordan, a strategist with Commonsense Ten. “But when we look back at the totality of it all we will still be outspent on electronic media six- or seven-to-one.”

In Florida, a review of records at the local NBC affiliate, WESH, shows that a succession of outside groups bought time for waves of anti-Kosmas advertisements, an anonymous, attack-ad relay race.

“They are not required to disclose who they are,” Ms. Kosmas said. “Therefore it’s impossible to connect them to their real agenda.”

Mr. Van Hollen sought to attach any Republican success on Election Day to the corporate benefactors backing the groups. “They are going to be very much indebted to these special interest groups that have come into these races,” he said.

In an e-mail, Representative Pete Sessions of Texas, the chairman of the National Republican Congressional Committee, accused Mr. Van Hollen of focusing on the anonymous donors as a way to “distract voters with scare tactics and side topics” rather than issues like jobs.

He added, “We appreciate the lawful work of any organization that is committed to working towards our goal of retiring Nancy Pelosi,” the House speaker.