Some of the longest backups on the Capital Beltway will get much worse this spring when Maryland begins a two-year project to rebuild part of the busiest stretch in the 64-mile loop, the segment between Colesville Road and Georgia Avenue.

State transportation officials have warned of "severe" disruption once they start the $17.3 million job of replacing and redecking four Beltway bridges approaching the end of their 40-year life. The project does not involve widening the highway.

While no lanes are to be closed during rush hour, crews will eliminate shoulders, narrow lanes and periodically shift traffic patterns, a recipe that has stymied traffic on roads that carry far less than the 250,000 vehicles a day that now travel this two-mile segment of the Beltway.

"The work zone will be a challenge for commuters," said Valerie Burnette Edgar, spokeswoman for the Maryland State Highway Administration. "We find that no matter what we're doing, even if we're not doing any work [at that moment], they slow down. And if a car breaks down, that would virtually bring it to a halt during rush hour."

The project represents the first stage in rebuilding bridges "that are coming of age" along the Maryland portion of the Beltway, according to Glenn C. Vaughan, head of the state's bridge design division.

But it will be just the latest frustration for Beltway commuters, who have seen congestion rapidly spreading along the northern part of the highway. A regional report issued two weeks ago found that the outer loop suffers severe tie-ups each morning over nearly the whole stretch from Interstate 95 to the Dulles Toll Road in Virginia.

"Oh my, what a pain in the neck," said Soila Aranda-Reyes, 31, of Silver Spring, when she learned of the upcoming project. "The traffic is going to be terrible. It's going to be very tough to get to work." She feared it would significantly lengthen the commute to her job as a housekeeper in Potomac, which now takes a half-hour in the morning and an hour in the evening.

"This area will be so crowded," said Yasir Abbadi, 28, who predicted the project would add as much as a half-hour to his daily commute from near Four Corners in Silver Spring to Washington. "I'm very upset, but what can I do?"

State officials said they were concerned that motorists might find this project especially irritating since it will not result in any more road capacity. "The only carrot we have is the safety of the Beltway," Edgar said.

The project is scheduled to begin in February with preliminary construction along Georgia Avenue, but motorists should not encounter delays until April, when crews from Cianbro Corp. of Maine begin Beltway work.

The job includes replacing the decks on two bridges over Brunett Avenue and Sligo Creek Parkway as well as redecking and partly rebuilding the Georgia Avenue bridge to better accommodate entering and exiting at the interchange. Crews also will erect a new span over the Northern Parkway foot and bicycle paths to replace a longer bridge initially built to pass over a planned highway that was never built.

Though the Maryland Department of Transportation is studying whether to add two new car-pool lanes to the existing eight-lane Beltway, the upcoming construction is not designed with any new lanes in mind, officials said. They said that the current bridge widths may already be able to handle two more lanes.

Nor could the state wait until a determination was made about whether to widen the Beltway, since bridges all along the highway are approaching the end of their expected lifespan, with those between Colesville Road and Georgia Avenue requiring the most immediate attention.

"It's kind of like triage," Vaughan said. "These are in worse shape, so these are the ones we attack first. These are showing signs they could create problems if we don't get out there and address them."

Work will proceed simultaneously on all the bridges and be conducted in a series of five phases, each lasting about four months. Each stage will entail a different traffic pattern, often forcing drivers to use the shoulders in place of ordinary travel lanes.

State engineers said they have tried to minimize the number of phases, though this will not provide construction crews with as much room to work as they would like.

"On some other projects, we've gone through more stages," Vaughan said. "In this particular case, the need to get in and get out is important to us as far as the impacts to the Beltway."

The state transportation department also is looking to ease congestion by introducing two new express bus routes this spring to connect Glenarden in Prince George's County with Bethesda and Silver Spring in Montgomery County.

Under the contract with Cianbro, the firm will hire a bus operator to run five Greyhound-style coaches to each destination each morning and provide return service in the evening, according to Len Foxwell, the department's director of Washington area transit services. The service will charge a $1 fare and cost $1 million a year to operate.

One route will begin in Glenarden at a commuter lot, yet to be announced, and stop in Riverdale before continuing to the Silver Spring Metro station. The other line will run from the Glenarden lot, stop at the National Institutes of Health and National Naval Medical Center and end at the Bethesda Metro station.

"There's a tremendous opportunity not only to provide transit services to mitigate traffic but also . . . to develop new transit ridership," Foxwell said. "There's really a double purpose here."

Commuters, meanwhile, are mapping out their own tactics for coping with the coming gridlock.

"I'll probably have to go the back ways to beat it," said Gary Ricketts, 38, who predicted the work would add 15 minutes to the commute between his Silver Spring home and Bethesda post office job. "And I won't be the only one taking back ways."

Rehabilitation of Beltway Bridges

A project to rebuild and redeck four deteriorating bridges along the Beltway between U.S. 29 (Colesville Road) and MD 97 (Georgia Avenue) is expected to severely affect traffic. The $17.3 million project will take two years to complete.

No lanes along the Beltway will be closed during rush hours. Lanes will be narrowed and shifted, and shoulders may be eliminated.

STAGE 1A

Replace and reconstruct right outside shoulder along I-495 between Georgia Ave. and Colesville Rd.

Timeline: April 2000 to July 2000.

Traffic impact: Moderate to severe.

STAGE 1B

Replace and reconstruct inside (left) shoulder and median barrier between Georgia Ave. and Colesville Rd.

Timeline: August 2000 to November 2000.

Traffic impact: Moderate to severe.

STAGE II

Begin replacing four bridge decks along I-495 between Georgia Ave. and Colesville Rd.

Timeline: November 2000 to May 2001.

Traffic impact: Moderate to severe.

STAGE III

Work to replace bridge decks continues as traffic is split around the work zone.

Timeline: May 2001 to August 2001.

Traffic impact: Severe.

STAGE IV

Work to complete the replacement of the bridge decks occurs as traffic is shifted to the right.

Timeline: August 2001 to November 2001.

Traffic impact: Moderate to severe.

SOURCE: Maryland Department of Transportation