The person spoke Tuesday at the baseball winter meetings under condition of anonymity because no deal was announced.
Washington had the best record in the majors last season. The NL East champions already have a formidable rotation led by Gio Gonzalez and Stephen Strasburg, and could boost it by adding Haren, an All-Star from 2007-09.
"I've got some young guys that act like veterans, and they pitched like veterans last year for me, and a veteran like Dan Haren is just going to make things even better,'' Nationals manager Davey Johnson said. "I think he's a great addition. I've seen him pitch a lot over the years, intense competitor, and hopefully we'll get that done.''
Haren was 12-13 with a 4.33 ERA in 30 starts and 176 2-3 innings for the Los Angeles Angels. The Angels nearly traded the 32-year-old righty to the Chicago Cubs for reliever Carlos Marmol after the season, then declined their $15.5 million option on him for next season and paid a $3.5 million buyout.
Johnson said he's fully familiar with Haren and says he might do even better in the NL.
"He pitched a lot of innings, and he had a decent year for Anaheim,'' Johnson said. "Also, the American League is a little bit tougher with an extra DH in there. I like his stuff. I like his competitiveness.''
Haren has made at least 30 starts in eight straight years. Known for his durability, he went on the disabled list for the first time in his career last season because of a back issue.
Johnson also predicted free-agent first baseman Adam LaRoche will re-sign with the Nationals.
"Adam LaRoche is going to come back,'' the manager said. "I mean, if I have to go to Kansas and take him and all his cattle to Florida, I will.''
Washington brought postseason baseball to the capital for the first time since 1933. After coming within a strike of advancing to the NL championship series on five different pitches, the Nationals lost to St. Louis in Game 5 of the NL division series.
"I think we're in a perfect position to show the world that we're a pretty good damn ballclub, and we can go farther into the postseason,'' Johnson said. "World Series or bust, that's probably the slogan this year. But I'm comfortable with that.''