* Government spokesman: door open if Wefaq wants to return
* Talks' success at risk if largest opposition group quits (Adds U.N. comment, paragraphs 11-12)
By Isabel Coles
DUBAI, July 18 (Reuters) - Bahrain's government expressed regret on Monday that the country's largest Shi'ite opposition group, Wefaq, planned to pull out of a national dialogue, but said political talks would continue with or without it.
The Gulf kingdom's Sunni rulers launched a national dialogue on July 2 to discuss reforms and address grievances after a four-month crackdown that began in March and crushed weeks of pro-democracy protests led by the Shi'ite majority.
A walkout by the influential opposition group could damage the dialogue's chances of reaching national consensus as sectarian tensions continue to simmer in the kingdom.
Protests have erupted almost daily in Shi'ite villages ringing the capital Manama since Bahrain lifted emergency law in June. Tension had been rising as demonstrators increasingly demanded that the opposition quit the talks.
The National Dialogue's spokesman, Isa Abdul Rahman, said Wefaq could rejoin the talks if it changed its mind.
"Should any participant choose to exclude themselves from the process, the door will remain open for them to return to the talks. Regardless of any participant's decision to leave the Dialogue will continue," he said.
Wefaq said on Sunday it would withdraw because its views were not being taken seriously in talks it accused of being dominated by pro-government representatives. That decision still has to be ratified by the movement's higher council.
Wefaq and six other political opposition groups, which were invited to take part in talks, have complained that their proposed political reforms would never be put into effect because the opposition received only 35 out of 300 seats at the talks.
Wefaq, which held more than 40 percent of seats in the country's elected lower council before it resigned in protest in February, was given five seats at the talks.
The government has defended its apportioning of representatives, saying it wants the dialogue to include all Bahrainis, whether they are involved in politics or not.
The United Nations said on Monday that Secretary-General Ban Ki-moon believes authorities in Bahrain need to create the right conditions so that as many people as possible, including Wefaq, can participate fully in the dialogue.
That would enable the dialogue to lead to "the kind of reforms that the Bahraini people are looking for," U.N. spokesman Martin Nesirky told reporters in New York.
Bahrain is seen as a fault line for tensions between Iran and Sunni Gulf Arab countries wary of protests spreading to their own Shi'ite minorities. The government has accused the opposition of pursuing a sectarian agenda with backing from nearby Shi'ite power Iran, charges the groups deny.
Mainstream opposition groups such as Wefaq have called for a more representative parliamentary system and greater powers for the elected lower council, whose powers are neutered by the upper Shura council, appointed by the king.
But hard liners calling for the abolition of the monarchy have gained popularity since the crackdown.
Dialogue spokesman Abdul Rahman said he was disappointed Wefaq had not stuck with the talks.
"It is sometimes harder to stay and help shape the solution than to walk away. Now is the moment to heal divides and unite behind a shared vision of Bahrain's future," Abdul Rahman said. "We consider al-Wefaq's contribution to the dialogue as central to its success thus far."
(Editing by Paul Taylor and Will Dunham)