The direct-mail solicitation reads exactly like an appeal from the National Republican Senatorial Committee.

“If we don’t act fast, get organized, and go on the offensive, the Democrats will solidify control of the Senate,” former Sen. Rick Santorum (Pa.) writes to his fellow Republicans.

But the four-page letter, full of red-meat rhetoric to mobilize conservative donors, is not a solicitation for the NRSC. Instead, it’s for a relatively new entity called the RNC Senate Fund. And its very existence appears to be news to both the NRSC and the Republican National Committee itself.

The RNC Senate Fund is not officially affiliated with the RNC, but it does have a connection. It was started by Chuck Yob, a longtime national committeeman from Michigan, and about 10 of his fellow RNC members.

Yob said the fundraising committee, which is raising hard federal dollars, wasn’t set up to compete with the NRSC, the RNC or any other official GOP entity.

“We’re just a supplement to everyone else,” he said.

Yob said the fund would contribute an undetermined amount of money to a finite number of GOP Senate — and House — candidates later in the cycle. He could not say how much money the committee had raised or what its fundraising goals for the rest of the cycle would be.

“It’s rolling pretty well along,” he said.

As the Republican Congressional fundraising committees lag far behind their Democratic counterparts in cash on hand, party stalwarts and interest groups are creating new money-raising entities to help offset NRSC and National Republican Congressional Committee shortfalls.

The RNC itself late last year created the 2008 Senate-RNC Victory Committee to raise money for one of the most vulnerable GOP Senators of the election cycle, John Sununu (N.H.). But that committee disbanded just a few weeks ago without having raised a penny, according to filings with the Federal Election Commission, because the fundraising events it was set up to organize never took place.

Still, Republican officials were sufficiently nonplused when told about the existence of the RNC Senate Fund this week that they are “taking a look” at the fundraising committee and making sure that it isn’t doing anything to make official donors believe it is connected to the national committee, according to a source familiar with the situation.

“It’s not even something that’s recognized by the RNC,” the source said.

In an interview, Santorum said he was happy to pen the fundraising letter when asked by the Senate fund’s leaders.

“I’m a former Senator. I’m just trying to help out my colleagues any way I can,” he said.

Santorum, who noted in the fundraising appeal that he was ousted in 2006 after being attacked relentlessly by Democrats, said he did not see Yob’s group as being in competition with the NRSC or any other official Republican fundraising committee.

“I’m certainly helping [Chairman] John Ensign [Nev.] over at the NRSC,” Santorum said. “John’s a very good friend. I’m certainly working with him closely to get resources there, too.”

According to GOP sources, the RNC Senate Fund now has a new fundraising letter in circulation, written by another vulnerable incumbent, Sen. Norm Coleman (Minn.). Coleman’s letter, they said, is an attack on Hollywood, and focuses on the amount of out-of-state money that his likely general election challenger, comedian Al Franken (D), has taken for his campaign.

Shira Toeplitz contributed to this report.