For the tens of thousands of commuters, beachgoers and other drivers who have wondered what the heck was going on at the the interchange of the Capital Beltway and Route 50, the answer will come Tuesday and Wednesday.

Or most of it, anyway. Maryland highway officials will open two of three newly constructed "flyover" ramps as part of the most expensive and complicated interchange rebuilding project in the state's $730 million widening of Route 50 between the Beltway and the Eastern Shore.

The $39 million Beltway interchange project will alter the traffic pattern for thousands of drivers and is expected to cause some immediate confusion Tuesday, in part because of a temporary detour.

"The traffic movements are completely different from anything people have done before at this interchange," said Rick O'Neal, the project coordinator.

The Route 50 interchange is one of the Beltway's busiest, carrying an average of 116,000 vehicles a day and thousands more on summer weekends when people go to and from the beach, often causing long backups.

The entire Route 50 project is scheduled to be finished in 1995, but that timetable may be extended.

The beginning of improvements from the Anne Arundel County line to Interstate 97 in Annapolis will be delayed for at least 45 days while state officials comply with Gov. William Donald Schaefer's order yesterday to find ways to deal with declining transportation revenue.

When completed, Route 50 will be a six-lane interstate highway from the Beltway to Annapolis, and a six-lane freeway from Annapolis to Queenstown on the Eastern Shore.

Maryland highway officials have been trying to shorten the beach trip, and the new interchange is expected to help.

On Nov. 28, officials opened two of the three eastbound lanes on the Kent Narrows Bridge, another bottleneck between Washington and Ocean City.

Beach traffic isn't the only problem.

During the evening rush hour, some traffic merging from Route 50 onto the Beltway must share lanes with traffic trying to exit the Beltway onto Route 50.

Morning rush-hour traffic often is slowed where westbound Route 50 drivers merge onto the Beltway.

To fix these problems, officials are replacing most of the existing exits and entrances with wider ramps, including the three flyover ramps that rise above the Beltway and Route 50 to deposit traffic directly onto the two highways.

The new flyover that could cause the most confusion Tuesday will carry traffic between eastbound Route 50 and the northbound Beltway.

Drivers heading in that direction usually take a looping exit just after passing over the Beltway. That exit will be closed on Tuesday.

But the new ramp, which is about a half-mile west of the current exit, won't be completed until Wednesday -- or later if the weather turns bad.

Drivers who want to go from east on Route 50 to north on the Beltway on Tuesday will be directed to take the southbound Beltway exit and go a few miles to Landover Road (Route 202). There they will exit and use a ramp taking them to the northbound Beltway.

"That's going to cause the most headaches," said O'Neal, adding that signs have been put up notifying drivers of the change. State police also will assist, but O'Neal urged drivers to avoid the area and find alternate routes.

The flyover ramp that will open Tuesday will carry southbound Beltway traffic to eastbound Route 50.

Those southbound drivers usually exit the Beltway just after passing underneath Route 50 onto a looping ramp that takes them to eastbound 50.

Now, they will exit the Beltway about a half-mile north of the existing exit, which will be closed.

By Saturday, O'Neal said, officials plan to open a new ramp carrying westbound Route 50 traffic to the northbound Beltway.

The third flyover ramp, to be opened next year, will carry westbound Route 50 traffic to the southbound lanes of the Beltway.

The project also includes the reconstruction and widening of the bridge carrying Route 50 over the Beltway, widening of the bridge on the Beltway over Amtrak tracks, and construction of a bridge that will carry traffic from Garden City Drive over Cobb Road and onto Route 50.