By Paul Hoskins and Jonathan Saul

DUBLIN, June 14 (Reuters) - Ireland's parliament met on Thursday to vote Prime Minister Bertie Ahern in for a third term as his new Green Party allies stressed policy differences would not get in the way of stable government.

"There will be a huge amount of tension throughout the five years, no one ever thought this would be easy," Green lawmaker Ciaran Cuffe told RTE Radio after his party voted late on Wednesday to enter government in Ireland for the first time.

"Have a clear list of deliverables and don't walk out the moment tensions rise," he said of advice received from other Greens who have served in governments in Germany and Finland.

Ahern's Fianna Fail emerged largely unscathed from May 24 national elections with 78 of 166 seats in the Dail (lower house of parliament) but needed new allies after its pro-business Progressive Democrat coalition partners suffered big losses.

Despite repeatedly attacking Ahern over his environmental and social record during last month's campaign, six Greens will back Ahern in Thursday's vote after agreeing a programme for government with him earlier this week.

Members of the Dail are expected to vote on a post-election prime minister at about 5 p.m. (1600 GMT).

Green support will give Ahern a slim majority but he is expected to bolster his position with the two remaining Progressive Democrats and by bringing in four independents.

That will also dilute the influence of any one partner and ensure that while the new government will have a greener hue, Fianna Fail's long-standing dominance as Ireland's biggest political party will likely be little impaired.

Although the Greens had to shelve some key policies in order get their first taste of power, including opposition to the use of Irish airports by U.S. troops bound for Iraq, Ahern has agreed to adopt some of their environmental priorities.

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