By Catherine Bremer

PARIS (Reuters) - French presidential frontrunner Francois Hollande has defended the idea of an unmarried first couple in the Elysee Palace if he wins the presidency on May 6, in what would be a potential break with protocol and tradition.

Asked whether he would wed longtime companion Valerie Trierweiler if he becomes president, the Socialist candidate said he had no intention of changing his principles to fit with tradition.

"You don't get married for reasons of protocol. Getting married is a choice," the 57 year old said during a live question-and-answer session with readers of regional daily Sud Ouest, which posted the debate online on Thursday.

"I will not do anything that runs counter to my principles," said Hollande, who had four children with his previous partner, former Socialist candidate Segolene Royal, but whom he never married during their 30-year relationship.

"I will present myself alone before the French. Alone. This is not a couple presenting itself but one person who must convince with his ideas, his approach. Then, you start work," Hollande said.

Hollande would be the first unmarried French president in recent history, although many of today's mainstream politicians are divorced and living with new partners. Many past presidents were known to have long-term mistresses.

Trierweiler is a divorced mother of three and a long-time reporter for the weekly current affairs magazine Paris Match, which she recently berated for running a cover story about her relationship with the presidential candidate.

A tall, elegant 47-year-old with a look reminiscent of late Hollywood actress Katharine Hepburn, she grew close to Hollande as reporter covering the Socialist Party when he was with Royal and she was with her former partner.

The pair have been together for several years now, but aides say that like many couples in countries where religious pressures to formalize unions are easing, they do not feel the need to marry.

"Hollande is a man of his time. He is not bound by convention," one of Hollande's inner circle of advisors told Reuters recently. "Like lots of French people, he's never been married and I don't think he feels the need to get married now."

Showing the change in attitudes since former Socialist president Francois Mitterrand ordered a cabinet minister and a top advisor to marry their girlfriends three decades ago, there had been no mutterings in the party about Hollande's civil status, the aide said.

Being a girlfriend rather than a wife would mean Trierweiler could not accompany Hollande to certain official functions with foreign heads of state. That may not rattle a woman who fully backs her man in politics but has her own life and career.

She gave up presenting a television show on the election so that she could take an active role in Hollande's campaign, but continues to cover cultural affairs and noted to a rival magazine that she still has to earn a living.

A recent opinion poll in Paris Match found that 40 percent of respondents wanted to see Hollande and Trierweiler as first couple versus 26 percent for Nicolas Sarkozy and Carla Bruni, a former supermodel who the conservative leader married a few months into his presidency.

(Writing by Catherine Bremer; Editing by Ben Harding)