NEW DELHI (REUTERS) - India's opposition Congress party is finding it hard to defend a long holiday taken by its vice-president Rahul Gandhi, and some seniors in the party are questioning whether the scion of the country's most famous family is interested in politics.

Mr Gandhi, a 44-year-old bachelor parliamentarian, took a leave of absence starting in late February, and is now said to be returning to work later this month. There is no word where he might be.

His vanishing act has spawned a series of tongue-in-cheek comments about his choice of holiday spot and what he might be doing, and "missing" posters have been pasted on walls in his rural constituency.

Jokes aside, Mr Gandhi's decision to go on a holiday at the start of a parliamentary session, at a time when Congress was attacking Prime Minister Narendra Modi over land policy, has led to doubts about his commitment to politics.

Senior Congress members, who normally pride themselves on displays of loyalty to the great grandson of India's first prime minister, are beginning to openly express frustration. "He's entitled to have a leave for a holiday, but the timing was wrong, because we had the budget session going on, and the issue of land acquisition was to be debated, he could have gone when there was a recess," party leader Digvijaya Singh said.

Mr Singh, who this week said Mr Gandhi would be back in time to lead a farmers' rally on April 19, was referring to Mr Modi's attempt to make it easier for industry to acquire land, a policy that Congress has called anti-farmer.

While Gandhi has been away, his mother, party president Sonia Gandhi, has taken full-time charge, leading a rally and visiting villages to protest against the land law.

In February, Congress said Rahul Gandhi needed time off to reflect on electoral defeats and plot the future of the party.

Many Congress party members want Mr Gandhi to take over from his mother, despite having led the party to its worst ever election defeat last year when he was chief campaigner against Modi.

Mr Gandhi's laid-back approach contrasts with the relentless work schedule of Modi, who claims never to take days off work.

One political cartoon published on Thursday showed a Congress member at an airport holding a placard bearing Rahul Gandhi's name, and saying he'd forgotten what he looked like. "It is very embarrassing for me as a Congress politician to justify Rahul's leave," said a senior leader who served as a minister in the Congress government voted out in May. "I did not join politics to defend his presence or absence."

His supporters say he will return fresh, and will modernise Congress when he takes over from his Italian-born mother.

Critics say the mystery vacation reinforces the image of a political lightweight, who makes periodic public appearances and retreats into a elite lifestyle. Even when he is officially at work, Mr Gandhi is more often spotted at an exclusive gym than in parliament.

Mr Singh said Mr Gandhi needed to become a full time politician. "He has to be. Politics...is not half time," Mr Singh told Reuters. He said he did not know where Mr Gandhi might be.