By Nick Carey and Timothy Mclaughlin

CHICAGO (Reuters) - Chicago Cubs baseball fans braced for the possibility that their team's quest for its first World Series title in 108 years might come to an end on Sunday, as police beefed up security ahead of a game that could clinch victory for the Cleveland Indians.

At Wrigley Field, the prevailing mood among Chicago's long-suffering fans was quiet and somber after a heart-wrenching 7-2 defeat at the hands of the Indians the night before, leaving the Cubs trailing 3-1 in the best-of-seven Fall Classic.

Tempers appeared to have cooled since Saturday night, when anger erupted after Chicago's Game 4 loss. Some fans, fearing that their "Loveable Losers" may blow the best chance to win professional baseball's biggest prize since 1908, vented their frustrations by kicking seats, ripping off their Cubs shirts or tossing their blue baseball caps in trash bins.

Some even became aggressive toward an overflow crowd of journalists seated outside Wrigley's small press box, voicing loud complaints about what they described as left-leaning media bias.

"To say we were very upset last night after waiting all our lives and our parents' lives for a championship would be an understatement," said Derek Eskew, 29, as he ate lunch a few blocks from Wrigley with friends.

"Look, we may win tonight, but even if we lose, we're just going to go to Wrigley and have some fun," he said.

Chicago's manager Joe Maddon had a word of encouragement for Cubs fans before the game.

"We are at the doorstep, the precipice of winning a World Series, absolutely," he said. "I understand the angst involved with that," the veteran manager said.

"We have to win tonight," he said. "It's up to us to get you beyond that moment and get back to Cleveland."

Outside Wrigley, police maintained a visible presence on Saturday night, with a loose cordon of officers seen around the stadium. A heavy contingent of officers in protective vests was stationed further away, awaiting orders in the unseasonably warm weather.

Police Superintendent Eddie Johnson said about 1,000 law enforcement officers were assigned to the area throughout the weekend.

"We are planning on a Cubs victory tonight, but either way we are ready," said Rich Guidice, first deputy director of the Office of the Emergency Management and Communications. "We have a good plan in place. The plan is for any type of circumstance that comes our way."

No major incidents involving fans followed Saturday's loss by the Cubs, he said. "The fans, for the most part, are behaving - behaving very well."

Losses by the Cubs in the third and fourth games of the series have sent ticket prices tumbling on the resale market.

The waning of the city's celebratory mood was reflected in demand for Game 5 tickets. By Sunday, tickets that sold for $3,000 or more the previous day had dropped to as low as $775 on online ticket marketplace StubHub.

The long queues to get into bars and restaurants around Wrigley Field on the previous two nights had evaporated on a cool overcast Sunday even as fans roamed the streets of Wrigleyville on Chicago's North Side.

CLEVELAND BUZZES WITH EXCITEMENT

Some 350 miles (563 km) to the east, a palpable sense of excitement gripped Cleveland, a city viewed as the doormat of professional sports until the Cavaliers, led by LeBron James, won the National Basketball Association's title in June.

Thousands of Indians fans have paid to watch Game Five over giant video screens at Cleveland's Progressive Field, hoping to celebrate their team clinching the World Series for the first time in 68 years.

For those unable to find a seat in the ballpark, nearby bars and restaurants offered their own viewing parties.

Messages of support flooded Twitter on Sunday via the hashtag #RallyTogether.

"Gotta love it when the priest ends mass by saying 'Go Tribe!' and everyone starts clapping! #RallyTogether," Cleveland TV news reporter Sarah Phinney wrote on Sunday.

Dan Gilbert, principal owner of the Cleveland Cavaliers, joked about the sudden turn of fortunes for the Ohio city's sports franchises. In June, the basketball team ended a 52-year major sports championship drought when they won the NBA title.

"It's been 141 days since Cleveland's last championship. @Indians have great opportunity to end that dry spell later today. #RallyTogether," Gilbert wrote on Twitter shortly after the Indians won Game 4 Saturday night.

(Reporting By Nick Carey and Timothy Mclaughlin, additional reporting by Steve Keating in Chicago and Jon Herskovitz in Austin; Editing by Alan Crosby and Nick Zieminski)