By Maria Sheahan and Hakan Erdem
BERLIN/SAARBRUECKEN, Germany (Reuters) - Chancellor Angela Merkel's conservatives strengthened their position as the largest party in the western state of Saarland in a regional vote on Sunday, bolstering her prospects of winning a fourth term in September's national election.
The election was the first of three regional votes ahead of the Sept. 24 federal vote and as such offered an opportunity for the parties to build -- or lose -- momentum in their quest to prevail at the national level.
Merkel's Christian Democrats (CDU) won 41 percent of the vote, up from 35.2 percent in the last election in Saarland in 2012, an exit poll for broadcaster ARD showed. The Social Democrats (SPD) won 29.5 percent, down from 30.6 percent.
"This is a of course a really great start to the election year of 2017," Michael Grosse-Broemer, one of Merkel's top deputies in parliament in Berlin, told ARD.
The dip in support for the SPD was a setback in its first electoral test under new leader Martin Schulz. He has re-energized the center-left party with a promise to tackle inequality that is resonating with many voters nationally.
Like federal Germany, Saarland has been governed by a 'grand coalition' of Merkel's conservatives and the SPD and that situation looked likely to continue as the result left the CDU short of sufficient support to rule alone in the state.
The SPD and the far-left Linke, which won 13 percent, also lacked enough votes to form a left-leaning coalition in the state assembly.
"Without the SPD there won't be a government in Saarland," Ralf Stegner, a Schulz ally and deputy SPD leader, told broadcaster ZDF, putting a brave face on the result.
Prior to the election, polls had indicated a left-leaning 'red-red-green' alliance of the SPD, the Linke and the environmentalist Greens -- or even a 'red-red' coalition if the Greens fail to win enough votes -- could emerge after the vote.
The Greens did not meet the 5 percent threshold required to enter the state assembly.
The SPD, Linke and Greens have discussed refraining from attacking each other during the national campaign. Schulz is trying to win over dissatisfied working class voters with a message of social justice.
(Editing by Catherine Evans)