CHICAGO (Reuters) -Delta Air Lines ( DAL ) on Thursday forecast quarterly revenue largely below expectations in anticipation of slower travel spending against the backdrop of the upcoming U.S. presidential election, sending its shares down 6% before the bell.

The carrier expects fourth-quarter revenue between $13.9 billion to $14.2 billion, compared to average analysts' estimate of $14.22 billion, according to LSEG data.

Delta also forecast adjusted profit of $1.60 to $1.85 per share in the quarter through December, whose midpoint was above expectations of $1.71.

"With an improving industry backdrop and strong demand for travel on Delta, we are positioned to finish the year strong," CEO Ed Bastian said.

Delta said the steps taken by U.S. airlines to moderate capacity improved its pricing power across all geographies in the third quarter. It expects the trend to continue in the December quarter.

An excess supply of airline seats in the domestic market during the summer travel season had forced carriers to discount fares to fill their planes, hurting their earnings.

U.S. airlines have moderated capacity since then. Annual domestic seat growth has slowed to 1.5% in October and November from 5.5% in July, according to analysts at BofA.

Capacity adjustments as well as a 25% year-on-year decline in jet fuel prices in North America have bolstered the industry's earnings outlook, driving up airline shares.

The NYSE Arca Airline index is up 25% since early August, outpacing an 8% jump in the S&P 500 index. Delta's shares have also gained 34%.

The U.S. carrier expects the Nov. 5 presidential election to shave 1 percentage point from its unit revenue in the December quarter. Its overall revenue is estimated to be up 2% to 4% in the quarter from a year ago on the back of a 3% to 4% increase in capacity.

Delta reported an adjusted profit of $1.50 per share in the September quarter, lower than the $1.52 estimated by analysts. Its earnings in the third quarter suffered due to mass flight cancellations following a global cyber outage.

A software update in July by global cybersecurity firm CrowdStrike triggered system problems for Microsoft customers, including many airlines. The disruptions persisted at Delta even as they subsided the next day at other major U.S. airlines.

Delta canceled about 7,000 flights over five days, disrupting the travel plans of 1.3 million customers. On Thursday, the company said the disruptions led to a 45 cents per share hit to its third-quarter earnings.

(Reporting by Rajesh Kumar Singh in Chicago and Abhijith Ganapavaram in Bengaluru; Editing by Chris Reese and Arun Koyyur)