On a clear, sunny day in November two years ago, John Engel and Fred Drasner climbed into a small, blue and white, single-engine Cessna and flew over Tysons Corner to check the traffic patterns on the highways below at rush hour.

Engel and Drasner were not local newsmen reporting on the daily traffic conditions on the Beltway -- they were attorneys from a D.C. law firm searching for the least congested area near Tysons Corner to locate their new branch office.

Away from the traffic bottlenecks, they spotted a pyramid-shaped building under construction on a road with immediate access to the Beltway, Route 66 and Dulles International Airport. Engel and Drasner landed in Leesburg, jumped into a car and drove to the spot, where they promptly began negotiating an office lease for their firm, Shaw, Pittman, Potts & Trowbridge.

Shaw, Pittman is one of a score of large urban law firms throughout the region that are moving to the suburbs of Northern Virginia, hoping to take advantage of the booming business growth there.

Some outside law firms are getting a foothold in Tysons Corner and Fairfax County by merging with the area's established firms. In the past year alone, a major Richmond firm and two large Baltimore law firms merged with Fairfax firms.

Other firms, such as the 144-lawyer D.C. firm of Shaw, Pittman, are opening branch offices in Northern Virginia to serve longtime clients there. "It's a natural extension for us," Engel said.

Fairfax County's Economic Development Authority reported that in fiscal 1983, 140 companies either relocated to or expanded in Northern Virginia, and last year 105 more announced plans to move to the area. More than a third are high-tech and telecommunications companies, according to Fairfax County executives. Many of the new companies are corporate headquarters for national firms.

And where big business goes, so go the lawyers.

"The attraction to Tysons Corner is clearly the phenomenal business growth in the area," said C. Thomas Hicks III, a partner at Shaw, Pittman.

One indication of the growth in the number of attorneys in Northern Virginia is the number of lawyers admitted to the Fairfax bar. That figure stands at 1,200 now, according to Tom Appler, president of the county's bar association. Appler said that for the past two or three years, the bar has been adding 15 to 20 new members a month. "This indicates fairly significant growth," he said.

Not all the lawyers who have moved to the area are members of the county bar, in which membership is voluntary. However, they must belong to the Virginia Bar Association.

"There's a tremendous amount of work out there -- real estate, defense contracting and high-tech business," said Jim Moore, a partner with Zuckerman, Spaeder, Moore, Taylor & Kolker, a D.C. firm that opened a Northern Virginia office two years ago. The Zuckerman, Spaeder branch in Fairfax, however, is an office rather than a full-service branch. "We opened it for the convenience to ourselves and our clients," Moore explained.

"With business growth, come people who need legal services," said Gerald R. Walsh of Miles & Stockbridge. "So, there is a great amount of legal work that flows with business coming in."

Miles & Stockbridge is a 123-lawyer Baltimore legal powerhouse founded in 1932. Last year it absorbed the remaining attorneys from Fairfax's McCandlish, Lillard, Rust & Church, a general business and litigation firm that had broken up rather than expand to develop a more specialized practice.

"We felt times were changing in the legal practice in Virginia," explained Walsh, who had been a partner of McCandlish, Lillard, Rust & Church for 14 years before joining Miles & Stockbridge. "With the tremendous economic growth in the area, we needed to merge with a firm that had a wider range of experience in security regulations, bond matters and sophisticated corporate practice."

At the same time, five other lawyers from McCandlish, Lillard joined the prestigious 241-lawyer Richmond firm of Hunton & Williams, the largest Virginia law firm, and established a new Fairfax office. By this summer, the Richmond firm expects to have about 11 attorneys in Fairfax.

It's clear that they now see the need to have a presence here to protect their turf," said Walsh of Miles & Stockbridge. "Bond work for municipalities and litigation are examples of work that used to be done almost exclusively by the three or four biggest Richmond firms but now are increasingly being done in Northern Virginia."

Attorneys at Hunton & Williams said that opening a Fairfax office was a natural expansion of their business because the firm has several clients in the area. One of its partners, for example, is the general counsel to the planned Center for Innovative Technology, which the state hopes will serve as a magnet for still more high-technology businesses.

"The basic reason we moved to Fairfax is that we had clients in Fairfax and there was also a great deal of new business here," said Michael Barr, a partner at Hunton & Williams.

Venable, Baetjer & Howard, a 100-year-old established Baltimore firm with about 150 lawyers, is another example of an urban firm moving into suburbia. Venable, Baetjer teamed up with a five-member Arlington firm, Dolan, Treanor, Murray & Walsh last year because of the "bright economic future" in Northern Virginia, said Gerard F. Treanor Jr., now a partner at Venable, Baetjer.

Merging urban and suburban law firms is not without its problems, and the difficulty of finding the perfect marriage between clients and practice has prevented some firms from consummating a deal.

"One firm might be representing plaintiffs in personal injury cases, while the other firm might be defending insurance companies involved in the very same personal injury cases," said Walsh. "Mixing different kinds of lawyers is also difficult because some attorneys may be more comfortable with a smaller firm. So, although merging may be the thing to do these days, it will be a measured phenomenon."

Another Baltimore-Northern Virginia connection is developing with the Baltimore firm of Frank, Bernstein, Conaway & Goldman, which also plans to open a Northern Virginia office, according to Legal Times, a legal publication based in Washington.

Along with Baltimore and Richmond firms, several D.C. firms have begun sniffing around the Northern Virginia suburbs, said Treanor. "The Potomac River just isn't the psychological barrier it once was for law firms," he added.

Hogan & Hartson, one of the largest D.C.-based firms with 192 attorneys, is "seriously contemplating" a move to Northern Virginia. "We have a number of clients there, and it would be a great time-saver for us to actually be there," said Bob Odle, administrative partner of the firm.

Attorneys at some of the established Northern Virginia firms said they view the increased competition as a challenge.

"We're going to give them a run for their money," said Michael F. Marino, a partner at Boothe, Prichard & Dudley, the largest Northern Virginia law firm. "We have the historical advantage of being here so long, and we have supplemented the newer legal areas at our firm. We think that we can compete head-on."

Boothe, Prichard has been in Fairfax City since 1892 and prides itself on being a "full-service" law firm. But even Boothe, Prichard wants to get a piece of the action at Tysons Corner and is moving there soon. "Over 500 corporations have moved into Tysons, so that's clearly where the action is," Marino said.

As recently as 10 years ago, much of Northern Virginia was suburban backwater. One of the few law firms at Tysons Corner, Lewis, Mitchell & Moore, was hidden in a wooded area on a two-lane country road when James Lewis founded the firm in 1968. And Fairfax City, the center of Northern Virginia's legal practice at the time, was a sleepy southern town when Hazel, Beckhorn and Hanes opened its law offices there the same year.

But in the past 17 years, Northern Virginia has become one of the region's hottest commercial and technological centers. A potential attraction to the area is the state-sponsored Center for Innovative Technology, which will coordinate university and corporate research and will be located on the Fairfax and Loudoun County line. It is scheduled to be completed next year.

Lawyers streaming to Northern Virginia will settle mainly in three areas, according to Walsh of Miles & Stockbridge: the Tysons Corner area, the intersection of routes 50 and 66 near the Fair Oaks Mall and the intersection of routes 123 and 66 near Oakton.

"Tysons Corner has the big firm, big town image," Walsh said. "At Fair Oaks, there is much development activity and high-tech companies. The intersection of routes 123 and 66 is attractive because of the good transportation and access to the Alexandria and Fairfax County courthouses rather than having to drive through the back roads."

Fairfax City used to be the hub of the legal community in Northern Virginia. "In the old days, young lawyers would go to Alexandria and Fairfax City," said David G. Lane, a partner at Lewis, Mitchell & Moore. The attractions of those areas -- courthouses and local government offices -- appear to have been surpassed by business opportunities elsewhere at the same time that increasing traffic has made the old legal centers less accessible.

Fairfax lawyers say there has been a "major exodus" from Fairfax City to other locations in the county. "Although it is near the county courthouse, the roads are getting more jammed and it has lost the old-time, old-town civility," explained Walsh. "People can't park there and get in to see you."

Walsh said that traffic congestion also is driving attorneys away from Bailey's Crossroads, Annandale and downtown Vienna, where there is a transportation gridlock.

Walsh speculated that in five to 10 years Reston will be another hub for lawyers, but now it's still too far off the beaten track.

With the burgeoning new business in Northern Virginia, the legal practice has changed dramatically. "It used to be that a generalist could practice law in Northern Virginia with confidence," said Treanor of Venable, Baetjer & Howard. "Now, the only way to effectively practice law there is to specialize and expand the capability of the law firm. It wasn't always so that you needed to have someone with government contracts expertise."

"There is more need now for the full-service law firm that has to be able to do everything well," added Duane W. Beckhorn of Fairfax's 38-lawyer firm of Hazel, Beckhorn and Hanes.

Another change that Northern Virginia attorneys note is the increasing number of national clients located in Northern Virginia. "The law firms that they look to are those equipped with the expertise and manpower to handle problems in places like Sunnyvale, Calif., as well as locally," said Treanor.

Some attorneys said that a Northern Virginia firm has competitive advantages over a D.C. firm because of lower rent and staff expenses. "This is important to the extent that people are shopping for price," said a lawyer at Zuckerman, Spaeder. But it appears to be the area's changing nature rather than the price advantage that is critical to attracting law firms.

"There is no longer a small-town atmosphere, with lawyers just representing the people they grew up with," said Moore of Zuckerman, Spaeder.