Assuming the deal is completed, sources say that Capps -- who was not tendered a contract by the Pittsburgh Pirates earlier this month -- would go to spring training as the presumptive favorite to be the Nationals' closer.
Capps' agent, Paul Kinzer, denied that an agreement has been reached. "We're still going over the offers and talking. It won't be until later tonight. We have not made a decision,'' Kinzer said.
Capps attracted interest from 16 clubs upon becoming a free agent 10 days ago. He narrowed his list of finalists to the Nationals and Chicago Cubs, and is expected to make his decision official Wednesday night.
Capps, 26, amassed 66 saves from 2007 through 2009 in Pittsburgh. But the right-hander's ERA spiked from 3.02 to 5.80 last season.
Washington is in desperate need of an upgrade to a bullpen that posted a 24-39 record and ranked last in the majors with a 5.09 ERA last season.
Information from ESPN The Magazine senior writer Buster Olney and ESPN.com's Jerry Crasnick was used this report.