Republicans must remain tightly unified around a core set of policy issues and themes, hammering at Democrats and the Obama administration on areas where they agree while avoiding divisive topics if they hope to duplicate their electoral successes of the past few months, Senate GOP leaders warned their colleagues Wednesday.

According to GOP aides and Republican lawmakers, the Senate Republican retreat, held at the Library of Congress, was designed largely as a way for Members to dissect their successes last year and discuss the best path forward this year.

One Republican said the meeting was positive but that leadership sought to stress the importance of learning the lessons from Democrats’ defeat in November’s gubernatorial elections in Virginia and New Jersey, as well as in Massachusetts’ special Senate election.

The “tone was upbeat but cognizant of the huge challenges facing the country. Voters are sending a loud message that they think the administration and Democratic Congress are proposing the wrong solutions to the wrong problems,— the Republican said.

“We talked about what got us here,— Sen. Richard Burr (N.C.) said following the meeting, adding that one of the key messages from leadership was that the Conference needs to continue finding specific policy areas where they can all work together and provide a united front.

“It’s much easier for Republicans to coalesce around good policy,— Burr said.

Senate Minority Leader Mitch McConnell (Ky.) used that basic strategy — focusing on areas of agreement and avoiding topics that caused rifts within his Conference as much as possible — effectively last year. Starting with the stimulus debate in which only a handful of Republicans defected to support Democratic proposals, McConnell laid out a careful strategy under which Republicans worked to frame the economic, national security and health care debates in such a way as to maximize Conference unity. Those efforts often prompted Democrats to all but abandon attempts at bipartisanship, making it easier to keep moderates such as Maine Sens. Olympia Snowe and Susan Collins in the fold.

Indeed, even as Republicans were gathering behind closed doors for their annual policy retreat, McConnell was opening a new front in the GOP’s war with Democrats, taking Attorney General Eric Holder to task for his handling of the Christmas Day bomber in a letter signed by Judiciary ranking member Jeff Sessions (Ala.), Intelligence Vice Chairman Kit Bond (Mo.), Homeland Security and Governmental Affairs ranking member Susan Collins and Armed Services ranking member John McCain (Ariz.).

GOP aides said McConnell’s strategy for this new offensive is based on his success in making the closure of the Guantánamo Bay, Cuba, prison camp one of President Barack Obama’s biggest political difficulties last year, using a mix of floor speeches, public events and critiques of the administration to raise the profile of the Christmas Day bomber issue.

But McConnell is also expanding the scope of his efforts, bringing other parts of the GOP into the messaging. For instance, Virginia Gov. Bob McDonnell wove the attempted Christmas Day bomber attacks into his response to Obama’s State of the Union speech Wednesday night.

“We have serious concerns over recent steps the administration has taken regarding suspected terrorists. Americans were shocked on Christmas Day to learn of the attempted bombing of a flight to Detroit. This foreign terror suspect was given the same legal rights as a U.S. citizen, and immediately stopped providing critical intelligence. As Sen.-elect Scott Brown [R-Mass.] says, we should be spending taxpayer dollars to defeat terrorists, not to protect them,— McDonnell said, according to prepared text of his remarks provided before the speech.

Meanwhile, the House Republican Conference is expecting three-fourths of its membership to attend a retreat in Baltimore later this week for a similar message.

Lawmakers are expected to depart for the Renaissance Baltimore Harborplace Hotel midday today and will return Saturday afternoon.

“As Americans in growing numbers are turning to House Republicans for solutions to our current crises, we expect another large gathering similar to last year,— said Mary Vought, a spokeswoman for Conference Chairman Mike Pence (Ind.).

The “Winning Back America— retreat is expected to be an intensive strategy session where lawmakers will focus on converting their political momentum into election victories later this year.

In addition to several small strategy sessions where lawmakers meet to discuss the best way to tackle a range of issues, Republicans will hear speeches from leaders and strategists who will talk to them about new ways for the party to harness power.

Friday’s featured speakers include former Speaker Newt Gingrich (Ga.) and former Notre Dame football coach Lou Holtz. Holtz, who is now an ESPN commentator, briefly considered running against Rep. Suzanne Kosmas (D-Fla.) last year but ultimately decided against it.

Obama will address Republicans on Friday afternoon.

Republican leaders said Wednesday that they would use the visit to reintroduce the president to their ideas on the economy, health care reform and other issues.

McDonnell and former House Majority Leader Dick Armey (Texas) will be the retreat’s keynote speakers on Saturday.

Now the chairman of FreedomWorks, Armey has become a leader in the grass-roots “tea party— movement — a group the GOP desperately wants on its side in 2010.