Metro plans to extend its morning rush-hour service on Monday for rail and bus passengers to accommodate federal workers who may be asked to report to their offices only to turn around and return home.

Spokeswoman Lisa Farbstein said the transit authority would essentially have “back-to-back rush-hour service.” There will not be a specific limit on how long Metro would maintain a higher level of rail service, including running eight-car trains, she said, but officials will monitor service and make adjustments. Metro considers 7:30 to 9 a.m. and 4:30 to 6 p.m. to be peak service hours. Peak fares would be limited to their normal times, she said.

“We’re not sure how many people we might have to accommodate -- if it takes an extra hour or two to get folks home,” Farbstein said.

On Monday, the rail service registered 770,840 trips, Farbstein said. Federal workers typically make up 40 percent of Metrorail’s rush-hour passengers, she said. The agency has estimated that a shutdown could reduce Metro ridership 5 to 20 percent.

Metrobus operators are also prepared to run extra service. However, Farbstein said the waits may be longer as the day progresses.

“It would be a very wise move for bus patrons to get into work a little earlier,” she said.

The biggest impact may be for MetroAccess customers, who make reservations for trips in advance. Those passengers should “reschedule as soon as possible,” Farbstein said.

“If they are required to vacate their office buildings, we don’t want to have an instance where people ... are waiting hours because their reservation wasn’t until 5 p.m.,” she said.

MetroAccess riders can make reservations by calling 301-562-5360 or book trips online on Metro’s Web site with a user ID.

The agency anticipates that the changes will necessitate paying train and bus operators overtime, but Metro did not have an estimate of the cost.

The Maryland Transit Administration says that its MARC trains and Commuter Bus service would operate as scheduled on Monday, and officials would assess the situation if the federal government makes an announcement this weekend. Officials would also review the need to reduce service if there is a prolonged shutdown, the MTA said.

Virginia Railway Express officials said they plan to run full service in the event of a shutdown.