Massachusetts Sen. John Kerry’s campaign for the Democratic presidential nomination continued to pick up institutional support Wednesday as the majority of retired Gen. Wesley Clark’s Congressional backers jumped on to his growing bandwagon.

Thirteen of Clark’s 18 House backers threw their support to Kerry, including Reps. Marion Berry (Ark.) and Charlie Rangel (N.Y.), the two leaders of the general’s forces on Capitol Hill. The announcement came just hours after Clark officially left the race.

“It is time to close ranks,” said Berry in an interview Wednesday. “We have a clear leader identified that we all think can make a good president.”

Of Clark’s House backers, only Reps. Martin Frost (Texas), Charlie Stenholm (Texas), Solomon Ortiz (Texas), Jim Matheson (Utah), and Gene Taylor (Miss.) did not immediately pledge their endorsement to Kerry.

In a meeting Wednesday morning, however, all but Frost voiced their support for Kerry and are expected to make official announcements in the coming days, according to well-placed Democratic sources.

The rush of Congressional support comes on the heels of Kerry’s convincing victories Tuesday in Tennessee and Virginia.

Clark’s third-place showing in Tennessee, where he had concentrated significant time and resources, led him to bow out of the race Wednesday in Little Rock.

“This is the end of the campaign for the presidency. … It’s not the end of the cause, because the real cause is the campaign for the future of America,” Clark said at the event.

The expected mass transfer of Clark supporters to Kerry coupled with Tuesday’s primary results seem likely to quiet a whisper campaign that the Massachusetts Senator could not win in the South — a region seen as crucial to Democrats’ hopes of unseating President Bush in November.

Clark’s supporters including many members of the Blue Dogs, a coalition of moderate to conservative Democrats largely clustered in the South.

“This is a sign of our continuing national appeal,” said Kerry deputy campaign manager Steve Elmendorf. “We won two Southern states and now we are starting to pick up Members in marginal, Southern districts.”

Berry said he has no concerns about Kerry’s ability to win in the South.

“This whole idea that it takes something special in the South I just don’t buy,” said Berry.

He pointed out that President John F. Kennedy — a Massachusetts Senator himself before winning the nation’s top office — was a personal hero and “did just fine in the South.”

In his 1960 presidential campaign against Richard Nixon, Kennedy won Alabama, Arkansas, Georgia, Louisiana, North Carolina, South Carolina and Texas.

In the intervening four decades, however, the South has turned into a Republican stronghold.

In the 2000 presidential election then-Vice President Al Gore won none of the seven states that Kennedy had carried 40 years before.

With Clark’s departure from the race Wednesday, the Democratic presidential field stands at five, half of what it was at its peak.

Kerry remains the prohibitive favorite for the nomination, although both former Vermont Gov. Howard Dean and North Carolina Sen. John Edwards have pledged to continue the race. Rep. Dennis Kucinich (Ohio) and the Rev. Al Sharpton round out the field.