This summer, for the first time in years, East Coast vacation travelers will probably be able to pass through this city without getting caught in steamy traffic jams. The Fort McHenry Tunnel, now in its sixth month of operation, has virtually eliminated such tie-ups, transportation officials said.

The new tunnel, running under the Patapsco River to complete Interstate Rte. 95 through Baltimore, has siphoned traffic from the old Harbor Tunnel and the Francis Scott Key Bridge. As a result, officials said, all three are expected to be free of bottlenecks, even during the travel season.

With four traffic lanes in each direction, the Fort McHenry Tunnel can accommodate up to 100,000 cars a day, more than double the number now using it.

"We're really moving traffic through here," said tunnel police Lt. Norman Boskind. "The place is so big it gobbles it up with very little trouble."

The Harbor Tunnel, for years a grimy bottleneck, is no longer choked with traffic, but its blighted image has suffered further by comparison to its gleaming counterpart.

This summer, however, the Harbor Tunnel will begin getting a facelift of its own. The two-year, $40 million renovation, is expected to begin in July. New roadway will be laid, lighting will be improved and the timeworn yellow tiles on the tunnel walls will be removed and replaced with white tiles.

But conditions at the Harbor Tunnel are going to get a lot worse before they get better. Work on each of the tunnel's two tubes is expected to take a year, and both northbound and southbound traffic will have to go through a single, two-lane tube during the renovation period.

"I'm not crazy about the idea," said Robert Alter, assistant administrator of the Maryland Transportation Authority, which will oversee the work.

Alter said his agency was planning a campaign to discourage motorists from using the Harbor Tunnel during the renovation period, and officials there hoped 15 percent or more of the 42,000 vehicles a day using the old tunnel can be diverted to the Fort McHenry Tunnel.

"The only way I'll be happy about it is if we can get 95 percent of the traffic out of there," Alter said.

In addition to eliminating traffic bottlenecks, the Fort McHenry Tunnel, which connects the marine terminal areas of Dundalk and Locust Point, has diverted some of the heavy truck traffic from downtown routes between those points, according to transportation officials.

Control of operations at the tunnel is centered in a massive room with banks of switches and dials and 64 monitor screens. The instruments there monitor carbon monoxide and vehicle speed.

In the tunnel, flashing signs alert motorists when they need to tune in police emergency broadcasts or public service messages.

There have been a few bugs to work out in the tunnel's early months of operation, but even when half its lanes are closed for maintenance or repairs, officials said, traffic moves at a steady clip.

Transportation Authority spokesman Tom Freburger said the design of the wide, brightly lit lanes of the Fort McHenry Tunnel had achieved its purpose, minimizing driver hesitation on approaching the tunnel. "I think people going through there are less tense," he said.

At the Harbor Tunnel, he said, drivers occasionally "freeze up" with tunnel phobia, and have to be driven or escorted by police through the tunnel.

"I don't think we've had one at the Fort McHenry," Freburger said.