Dave Biddle, a computer technician with the D.C. police department, arrives at work an hour early every day to mine gold near police headquarters at Third Street NW.

The treasure he seeks is free parking, and in a quarter-mile-long depression known on city maps as I-395, and lovingly referred to by Biddle and hundreds of other government employes as "The Pit," it's up for grabs to anyone willing to be there at 6 a.m. to stake a claim.

For more than a decade, city officials have promised a connecting road to link the Southwest Freeway and New York Avenue. For more than a decade, the last quarter mile of this $165 million highway known to planners as the Center Leg has been and remains the most expensive public parking lot in the city: The Pit.

But for some tiles and asphalt to finish a tunnel under Massachussetts Avenue, this stretch of concrete would be linking motorists to two of the city's busiest arteries.

As it stands, government and construction workers line up in the early hours to vie for a coveted patch of pavement, while narrow side streets nearby are flooded with commutersdetoured around the closed highway link.

It may be two years yet, officials said, before the project is completed and the road opened. Meanwhile, city transportation department employes have staked out their own free parking in half the tunnel under Massachusetts Avenue, while the other half is filled with tour buses, and signs on the completed on- and off-ramps at New York Avenue mark the underpass as strictly off limits to the public.

Lamposts have been erected along the 700-foot-long New York Avenue ramps, but they are all broken. Across the mouth of the tunnel stretches a chain link fence and gate 13 feet tall.

Why is the connector still blocked off?

"The roadway in the tunnel needs a layer of asphalt," said Wallace Cohen, the city's deputy assistant director for transportation planning. "And the tiles on the tunnel walls are still missing. After that, it's finished."

The city has asked Congress for about $18 million in matching funds to finish the project, but has so far failed to get the money. Only a small part of those funds, Cohen said, is needed for the asphalt and tiles. Most of it is to pay debts the city incurred building the tunnel in the first place.

Half of the six-lane tunnel was turned over to U.S. Capitol police last Semptember to park tour buses, which were banned at the same time from Pennsylvania Avenue near the Capitol and the White House.

The other half of the tunnel, with space for more than 100 passenger cars, also is fenced off with an "Authorized Personnel Only" sign. Here, employes from the parking bureau two blocks away pull past the gate in their blue and white patrol cars--or are dropped off by coworkers--each afternoon to exchange the vehicles for their own cars, which they park there for free in the morning.

"I suspect there's a lot of police in there also," said parking bureau chief Fred Caponiti. In any case, he said, "they're not the ones who determine when the road opens up."

Originally, the Center Leg was part of a grandiose plan to build several highways through the city, crisscrossing the downtown and connecting the inner core with major roads in the suburbs. Those plans were scrapped in favor of increased funding for Metro, however, leaving the Center Leg proposed as a quick underground way to drive across the Mall.

Failure to open the New York entrance and exit has meant congestion for Second and Third streets, which run parallel to the freeway. Both streets, said Cohen, "are a mess. The roads really weren't meant to take that kind of volume" generated by the expressway.

Located near the closed road are police headquarters, the courts and many other local and federal government offices. For many people who work there, every delay in transforming The Pit into the highway is a blessing.

By anyone's measure, the parking fee is practically a gift: 25 cents for three hours, the only such long-term rate in the downtown area. But a count this week showed that more than half the 200 parking meters originally installed on the six-lane lot are missing.

It is for those free spaces that Biddle and others line up before dawn, steering their pickups, vans, Bugs and sedans off Third Street and into The Pit.

Many sit and snooze in their cars until the morning work shift begins. Biddle, who used to start work at 7:30 a.m., was granted a half-hour alteration in his schedule so he could still get his parking spot at 6 and have less time left over to kill in The Pit.

"It's either that or pay $3 to $5 on one of the lots," said Biddle, sitting behind the wheel of his '72 Plymouth Valiant one recent afternoon on his way home. Besides, "The parking lots are all closing. There's one left up on the corner. When they close that, God knows where we're gonna park."