LA PAZ, Bolivia — President Evo Morales’s bid to run for another term by amending the constitution appeared headed toward a slim electoral defeat Sunday, according to unofficial partial vote counts and early results.

Morales has governed for a decade and, while still popular, many Bolivians have tired of corruption in the ruling elite and have shown, especially in recent in municipal elections, an eagerness for fresh faces.

A ‘‘yes’’ vote in Sunday’s referendum would have let Bolivia’s first indigenous president seek a fourth term in 2019.

Two unofficial ‘‘quick counts’’ of sample voting stations by polling firms put the ‘‘no’’ vote slightly ahead. The Ipsos-Apoyo firm had it leading 52 percent to 48 percent, based on counted ballots at one of every 15 polling stations.

Michael Shifter, president of the Inter-American Dialogue think tank in Washington, called the tight vote a surprising and major blow for Morales, who won reelection in 2014 with more than 60 percent of the vote.

Morales, who entered politics as a coca growers union leader, could now be motivated to groom a successor, Shifter said.

Pre-election polls said voters who had decided were evenly split on the change, while about 15 percent were undecided.

Associated Press