* Far right to promote Navy Blue bloc with UMP mired in feud
* UMP brass to be on show in parliament questions on TV
* Third "non-aligned" wing bolts from Fillon, Cope groups
PARIS, Dec 4 (Reuters) - With the mainstream conservative UMP opposition party at risk of imploding in a leadership feud, France's far-right National Front will urge disillusioned centre-right voters on Tuesday to switch to its "Navy Blue" patriotic grouping.
As the UMP appears on televised parliamentary questions split for the first time into rival political blocs, National Front leader Marine Le Pen will be in a nearby room promoting a coalition she hopes will boost conservative votes for her party.
The National Front won a parliamentary seat in June for the first time since the mid-1980s and Le Pen has boasted of a rush in applications to join the party since the UMP collapsed into internal wrangling six months after losing power in May.
She will roll out membership cards on Tuesday for a group launched early this year that lets conservatives of all shades, including tentative nationalists and UMP deserters, rally to her cause without having to actually join an anti-immigrant party.
Voter anger over what has become a farcical feud between moderate Francois Fillon and hardliner Jean-Francois Cope to lead the UMP could be reflected in parliamentary by-elections and in local elections in early 2014.
"I think we are going to have a very nice surprise in the by-elections because there is a desire on the part of UMP voters to sanction what is going on," Le Pen told Radio Classique.
"Some will abstain and many will vote for National Front candidates because we seem today to be the only ones who can defend them and represent an opposition to the government."
The National Front scored a surprise 18 percent in the first round of the presidential election in April. There are three by-elections for parliamentary seats coming up before year-end; the National Front may score well but not enough to win a seat.
Cope, a disciple of former president Nicolas Sarkozy and his hard line on immigration, and Fillon, Sarkozy's more moderate former prime minister, were meeting for a second day to try and resolve a two-week standoff that has clouded the UMP's future.
Cope has twice been announced the winner of a Nov. 18 leadership contest, but Fillon has demanded a fresh vote be held. Both candidates initially claimed victory and accused the other of vote-rigging.
The pair briefly agreed last week to call a party referendum on whether to hold a fresh vote, but descended into bickering again over Fillon's forming of a breakaway wing in parliament.
Sarkozy got his fingers burned when he attempted to mediate last week, brokering a truce that lasted just a matter of hours.
The UMP, which held power for a decade until Socialist President Francois Hollande's victory in May, will appear at question time with the breakaway wing of lawmakers loyal to Fillon standing in defiance to Cope as party leader.
"They need to take a decision because we are at a stalemate.
We cannot go on like this, it's not tenable politically," Henri Guaino, a former aide to Sarkozy, told BFM TV.
"We cannot have a leader who is contested by half of the party. And we cannot have a party with two parliamentary groups. It's the ultimate in absurdity."
The rift in the UMP, founded by Jacques Chirac in 2002 to try and glue together different right-wing groups, has worsened in recent days with a new faction of "non-aligned" conservatives joining forces and refusing to back either Cope or Fillon.
Bruno Le Maire, a farm minister under Sarkozy who planned to hold a meeting of the "non-aligned" faction on Tuesday, said that even if Fillon and Cope managed to come to an agreement, there still needed to be some kind of vote by party members.
"We need to make sure this crisis does not get decided by a little arrangement between friends, like we've seen in the past," Le Maire told France Info radio.