It might just be the ultimate insiders’ strategy: When pressing a client’s cause, try to catch the ear of the two offices that Congress most cares about to spread your message.

This duo of influential outposts isn’t the House and Senate leadership. Rather, Hill staffers’ most valuable sources of information are the Congressional Research Service and the Congressional Budget Office.

That’s according to research done by ex-K Streeter David Rehr, who holds a doctorate in economics and is now an adjunct professor with George Washington University’s graduate school of political management.

If you’re a lobbyist and you’ve never tried to cultivate the CRS or the CBO, you might be missing out, Rehr says. Just don’t expect it to be easy.

“I’m a little surprised that people don’t naturally think of CRS or CBO as part of the process,” Rehr said recently. “And I think the one thing the research said to me: They’re more important in the process than we probably realized.”

Rehr’s survey of bipartisan aides on Capitol Hill found that 55 percent rated the CRS’ information as “very valuable,” the most of any source. They ranked the CBO third — after academic and issue experts — at 32 percent.

These findings don’t match up with the sources that lobbyists think Hill aides find most important, Rehr’s research showed. Neither the CRS nor the CBO even registered among lobbyists’ top 5.

“It’s a little harder in the culture of advocacy because if you’re not used to doing it, you do what’s easier for you,” Rehr said. “If you were a Hill staffer, now you lobby staff and members.”

Michael Fulton, a longtime lobbyist who is with the Arnold Agency, recently heard Rehr’s pitch and said the idea clicked with him because he relied on CRS reports when he worked on Capitol Hill.

“My daughter works on the Hill, and she lives by them, and I used to live by them when I was on the Hill,” Fulton said. “I think if a CRS report has any inaccuracies or is leaning away from your client’s perspective, it would be valuable to correct that sooner rather than later.”

When it comes to dealing with the numbers-driven, wonky CBO, lobbyists caution that if you don’t have the data to back up a client position, it’s probably not worth the stop.

“It’s not really lobbying, it’s educating,” said one veteran health care lobbyist. This K Streeter noted that the CBO, which “scores” how much each piece of legislation will cost, is less interested in meeting with lobbyists or the Washington representatives of corporations and instead wants high-level executives, actuaries or economists who speak their language.

“People don’t approach them lightly or approach them ever without an outside numbers run or solid policy arguments that would shape a score,” this lobbyist said. “They’re going to dig, and they’re going to find the answer.”

A spokeswoman for the CBO referred me to its website, which explains that in preparing its cost estimates and other analysis, “CBO uses data and other information from a wide variety of sources, including federal agencies, state and local governments, and industry groups, among others. CBO closely follows professional developments in economics and related disciplines, encourages open discussion of analytic issues, and consults with outside experts in a broad range of relevant fields for guidance on ongoing work.”

Lobbyists who’ve worked with the CRS, a branch of the Library of Congress, say it can at times seem more shrouded in mystery and potentially more difficult to navigate as an outsider with an agenda. Many of the CRS reports are private and come only at the request of a member of Congress.

“I think the better way to go is to have a congressional champion who then writes to the CRS,” Rehr said. It’s also crucial to identify the researcher who handles the topic your clients care about.

“You’ll see who wrote the CRS report, and you find out you knew them from GW or American [University],” Fulton said.

Then, you can make the connection directly.

“CRS experts use available information from a wide variety of sources, on all sides of issues, enabling them to serve Congress with comprehensive, authoritative, objective and nonpartisan research and analysis,” CRS Communications Specialist Cory Langley wrote in an email.

Rehr said the research service is “less numerical” than the CBO, “so they’re even more open to data and empirical studies that help them do their job better.”

Still, said Rehr, the former head of the National Beer Wholesalers Association, it’s not as if you could hand a CRS researcher a study on beer taxes and they’ll include it in one of their reports. “But it might influence the report,” he said.

And a CRS or CBO mention that isn’t negative means ready-made talking points, one-pagers and potential fodder for issue advertising.

“Sometimes you get some favorable paragraphs or a reference, then you can pull that out and create lobbying material,” Rehr said.  “It gives you a little more oomph.”