Jeff Parke (Philadelphia Union photo)

D.C. United traded for a second veteran central defender Tuesday, acquiring Jeff Parke from the Philadelphia Union for defender Ethan White. The clubs also swapped places in MLS’s allocation order, with United relinquishing the top slot for the No. 6 position.

“Our priority was to get another starting center back, and that is not easy in this league,” United General Manager Dave Kasper said. Parke  “instantly upgrades our backline.”

Parke, 31, replaces Dejan Jakovic on the roster and will partner with Bobby Boswell, whom United acquired in the MLS re-entry draft last month.

Jakovic’s transfer to a Japanese club was finalized this week, ending a five-year stay in Washington. Last season Parke made $205,000, Jakovic $280,000.

With preseason camp opening in two weeks, United was not comfortable with the other starting options in the heart of defense: White, 23; Conor Shanosky 22; and Nana Attakora, 24.

Parke has started 234 regular season matches since entering the league as the last pick of the 2004 college draft. He played in New York for five years, and after one season with lower-tier Vancouver, spent three with Seattle and one in Philadelphia.

In 2008, he and New York teammate Jon Conway were suspended by MLS for 10 games after testing positive for a banned performance-enhancing substance.

This offseason, Parke requested a trade, though the reason is unclear. In the Union’s news release Tuesday, the Abington, Pa., native and Drexel graduate is quoted as saying: “For reasons that I can only describe as a personal matter, I am leaving my home town and this great club. This has been an extremely difficult decision for me.”

Parke turns 32 in March. Boswell will be 31 in March.

Asked about their ages, Kasper said: “It’s a position that requires experience and intelligence. Both are at a great age with many years left at a high level.”

White was a homegrown signing from Bethesda-Chevy Chase High School and the University of Maryland. He started 21 league matches as a rookie in 2011, did not make any regular season appearances in 2012 and had 13 starts last season. He has been hampered by injuries throughout his career.

On his Twitter page, White thanked the fans and organization. In Philadelphia, he will reunite with former Maryland teammates Zac MacMath and Matt Kassel.

In essence, United replaced Jakovic with Parke; White with Attakora, who served with Toronto and San Jose; and Brandon McDonald with Boswell. McDonald was traded to Real Salt Lake last summer but most of his contract remained on United’s books.

This winter, United also acquired three other defenders: Sean Franklin, who will start at right back; Attakora, who will provide central depth; and right back Jalen Robinson, a homegrown signing from the Baltimore area and Wake Forest.

The other facet of the trade was the swapping of allocation slots. United figured to use the top position to claim a player such as Guatemalan midfielder Marco Pappa, a former Chicago star who is negotiating to return to MLS after a short tenure in the Dutch league. U.S. national team midfielder Maurice Edu also might return. However, after a series of moves upgrading the backline and acquiring U.S. national team forward Eddie Johnson, United probably does not have the resources to afford Pappa or Edu.

Pappa would likely earn $300,000. Edu is making an estimated $1.3 million at Stoke City in the Premier League. His representatives are seeking a loan in Europe, but should he return to MLS, the former Maryland star would require a designated player contract (probably at least $500,000).

Philadelphia is angling to acquire Edu and wanted the top allocation slot to improve its chances, multiple sources said.

Why would Edu go through allocation when high-profile Americans Michael Bradley (Toronto) and Clint Dempsey (Seattle) were exempt from the process? Like that pair, Edu would also be a designated player and have no lingering ties to an MLS team. However, league headquarters would not help facilitate Edu’s re-acquisition by paying a portion of a transfer fee; he would move on a free transfer. In such cases, MLS utilizes the allocation ranking, regardless of whether the player signs a designated player contract.

If both Edu (Philadelphia) and Pappa (to Seattle in the No. 2 allocation slot) sign with MLS and go through allocation, United would move up to the No. 4 slot ahead of possible signings this spring and summer.

How will the acquisition of Parke impact United’s decision about the No. 1 pick in Thursday’s SuperDraft in Philly?

There are several ways to look at it:

With Boswell, Parke, Attakora and Shanosky, central defense now seems firm, diminishing the chances United would select either of Cal’s coveted center backs, Steve Birnbaum or Christian Dean. In which case, Maryland forward Patrick Mullins‘s rises to the top of the list. Then again, the club may opt to groom a Cal back for a prominent role in the coming years. Dean can also play left back — a position where United lacks depth.

Another angle to it: Dean is a Generation Adidas signing and would not count against the salary cap right away. As seniors, Birnbaum and Mullins would.

In other news, Kasper said United is in the “final stages of negotiations” with Argentine forward Fabian Espindola (28 goals and 12 assists the previous three seasons). United acquired his rights in the second stage of the re-entry draft last month.