* UFO union calls on its members to strike from 0300 GMT to 1100 GMT
* UFO union says strike could continue for very long time
* Lufthansa says will cancel 25 pct of flights during strike
* Lufthansa shares close up 0.5 percent, DAX index down 1.6 pct (Adds Lufthansa comment, paragraph 4)
By Peter Maushagen
FRANKFURT, Aug 30 Lufthansa passengers face widespread flight disruption from Friday after cabin crew representatives said they would start a series of strikes over pay and cost-cutting measures at Germany's largest airline.
The UFO union, which represents around two-thirds of Lufthansa's 19,000 cabin crew, late on Thursday called on its members to strike from 0300 GMT to 1100 GMT on Friday in Frankfurt.
"UFO calls on its members within Lufthansa to participate in the strike in Frankfurt from 0500 to 1300 hours (local)," UFO said in an emailed statement.
Lufthansa plans to cancel 64 flights, or 25 percent of the flights during the duration of the strike, a spokesman said.
The strike would also lead to "unplanned delays", the company said in a statement on its website. The airline planned to operate a total of 840 flights on Friday.
Financial Times Deutschland had reported before cabin crew members were preparing to hold the strikes in Frankfurt and Munich, citing UFO sources. It said on its website the union was discussing whether the strikes would also include Berlin.
The strikes come as Lufthansa cuts jobs and implements a three-year cost-cutting programme to boost margins and finance investment in planes in the face of a weakening economy, high fuel costs and increased competition from low-cost carriers.
Germany's leading airline, which operates around 1,850 flights daily mostly from Frankfurt and Munich, needs to generate more profit to pay for 17 billion euros ($21 billion) of more fuel-efficient aircraft on order.
Lufthansa and the UFO union have been negotiating for 13 months, with the union demanding a 5 percent pay rise and guarantees that Lufthansa will not outsource jobs and use more temporary workers, as it has already done in Berlin.
Talks broke down on Tuesday, and while Lufthansa has called for further negotiations, it maintains that cabin crew must contribute to the cost-cutting programme.
"It may well be that this industrial action could continue for a very long time," UFO said on its website.
UFO said the first wave of strikes would cover certain airports, rather than nationwide action. It has previously mentioned Berlin, Frankfurt and Munich as likely candidates.
"We do not want to give Lufthansa the opportunity to prepare for the strike by getting replacement crews ready," UFO head Nicoley Baublies told Reuters.
Lufthansa has previously said it would seek to keep disruptions to a minimum by using cabin crew who were not part of the union and by drafting staff from other units.
A spokesman for the airline said it had several strategies to mitigate the impact of striking staff and would prioritise long-haul flights.
Lufthansa estimates a nationwide strike on a busy day would cost it millions of euros. Analysts have said costs could be kept to around 5 million euros a day if flight cancellations were kept to a few hundred.
($1 = 0.7982 euro) (Reporting by Marilyn Gerlach, Peter Maushagen and Peter Dinkloh; Editing by Mark Potter, Helen Massy-Beresford and Leslie Gevirtz)