* Mediator Brahmin still working for peace talks
* Events "pointing in the opposite direction"
* Syria crowding out other crises in U.N. aid budget
By Tom Miles
GENEVA, April 23 (Reuters) - Hopes for a political deal to end Syria's war are fading and it is getting harder every day to send aid to millions of trapped and displaced civilians, U.N. humanitarian chief Valerie Amos said on Wednesday.
The United Nations has long said negotiations are the only way to resolve a conflict that is destabilising the region, but peace talks chaired by mediator Lakhdar Brahimi this year foundered after two rounds.
Syrian President Bashar al-Assad's decision to hold a presidential election in June - which he is widely expected to win - has further undermined Brahimi's hope of agreeing a change in leadership.
"We're into the fourth year and this is a conflict that could go on and on and on ... It feels as though we're no nearer getting to that political solution," Amos told Reuters in an interview in Geneva.
Efforts to resolve the conflict have been repeatedly stymied by divisions between the Syrian government's main ally Russia and other veto-wielding members of the U.N. Security Council.
Those divisions have only got deeper since Brahimi's peace talks fell apart in February, with talk of a "new Cold War" over Russia's annexation of the Ukrainian region of Crimea.
Brahimi "is continuing to work tirelessly behind the scenes to try and bring the (Syrian) parties together. Whether or not he will be able to do that, I think at this point I'm not sure that he knows whether he will succeed," Amos said.
"There are many external factors that seem to be pointing in the opposite direction," she added.
Amos and four other heads of U.N. agencies renewed their appeal on Wednesday for all parties to end the conflict and warned that the "worst days are yet to come".
Amos said their joint statement showed that all five were "deeply frustrated at the lack of movement" in Syria.
"The humanitarian situation is deteriorating day by day. It's getting harder and harder for us to reach the people that are in desperate need in some parts of the country," she added.
"We've tried for the last week to negotiate to be able to bring some supplies across the conflict lines in Aleppo and were not able to do that. The team in fact got stuck in Aleppo and couldn't leave because the road back to Homs and then back down to Damascus was under fire."
Amos said the cost of feeding, protecting, aiding and educating Syrians, was leaving less U.N. aid money for other crises.
Syria's needs this year are estimated at $6.5 billion, she said.
"Even if we get all of that, it sucks money out of other parts of the system," Amos said. "What is left for these other major crises becomes much less."
Among the most acute crises are two neighbouring African war zones - Central African Republic and South Sudan. (Reporting by Tom Miles)