Until a few months ago, Lakeland Aviation was the equivalent of a mom-and-pop business in the commuter airline industry.

For Steven and Linda Van Beek, Lakeland's president and vice president, the workday began at 5 a.m. and seldom ended before 10 p.m., seven days a week.

Besides being president, Steven Van Beek was the pilot and baggage handler and practically everything in between.

He ferried his rented Beechcraft Baron four times daily between Rice Lake, Wis., and Minneapolis. "We handled our own tickets. He carried the passengers' baggage to and from the plane, he did everything," including cleaning and fueling the small craft, recalled Linda Van Beek. "I worked right alongside him," she said.

Within the past year the Van Beeks have expanded their business with the purchase of 10 planes, and Lakeland, which now has 16 employes, flies commuter routes covering northern Wisconsin, Minnesota and Illinois.

"It's a struggle but our business is growing," Linda Van Beek says.

A few of the 280 commuter airlines are still little more than one-man operations, but rapid growth in the industry in the past two years has made them all but a vanishing breed.

"The competition will eat up the one-man show," said Richard A. Henson, president of Henson Airlines, Salisbury, Md.

Henson, a pioneer in the commuter airline industry, said, "We had to fight our way at first, because we weren't accepted very well."

Moreover, standards have changed and the commuters will have to meet them "if you're going to replace the carriers that are moving out," said Henson.

"It's an industry with tremendous growth potential," said David R. Forward, president of Denver-based Pioneer Airlines.

On the other hand, said Forward, the business hasn't been the bonanza that some entrepreneurs had expected. Although it's relatively easy to buy an airplane, he said, "it's tough to break even and make a go of it."

It's especially tough for the commuter airlines now because of the air traffic controllers' strike, which is affecting travel patterns. But despite this temporary setback, the general mood of the commuter segment is one of optimism for significant growth, mainly spurred by deregulation of the airline industry that began three years ago. A spokesman for the Civil Aeronautics Board said 30 to 40 commuters have been granted certificates since deregulation.

The typical commuter airline operates flights covering what the industry calls short-haul markets. Most flights are no more than 250 miles.

Commuter airlines operate propeller-driven or turboprop planes that seat 60 or fewer persons, and make regularly scheduled flights in support of the CAB's "essential air service" program.

The CAB program provides for continuation of air transportation for 10 years to all cities authorized for service on Oct. 28, 1978, when deregulation became effective. A community qualifies for essential air service when the last major air carrier proposes to curtail or cease scheduled flights.

The CAB then looks for a replacement carrier to provide minimum essential service to that community.

About 330 cities in the contiguous 48 states and Hawaii are covered by the program, and more than 200 of those are served by commuters, according to the Commuter Airline Association of America (CAA).

Commuter airlines transported 9.5 million passengers in 1978, and CAA projects 15 million this year.

"We expect a 10 to 15 percent rate of growth the rest of this decade," said Alan Stephen, CAA vice president for operations.

"The number of passengers carried by commuters will be quadrupled over the decade, even though air travel is forecast to increase at an annual rate of 4 to 5 percent," estimated Samuel Colwell, director of market planning at Fairchild Industries Inc., a major manufacturer of commuter aircraft.

(Despite the commuters' rapid growth, they still carry less than 1 percent of the traffic, Colwell said.)

Fairchild concluded some time ago that the commuter market would explode, and has entered a joint venture with Saab of Sweden to build a new generation of planes to serve that market.

With the exception of high-density markets such as Washington and New York, all short-haul service will be performed by commuters, Stephen of CAA predicted.

He pointed out that the major carriers prefer to operate long-haul flights and are taking advantage of deregulation by pulling out of cities where passenger volume has shrunk.

"It's not good business to land a big jet to pick up two people," said Herschel Connell, vice president of Colgan Airways of Manassas, Va.

In the midst of this growth spurt, however, the commuter industry has been caught in the crosswinds of the controllers strike. Like the giants of the airline industry, most of the commuters have been forced to cut back their operations, and some have been forced to liquidate.

In many instances, potential commuter passengers, worried that they might miss connections as schedules change during the strike, have opted to drive the relatively short distance usually flown.

But the strike has not seriously disrupted service for the more conservative commuter airlines that have structured their business to withstand cyclical or sudden changes in the marketplace.

Colgan Airways, which operates 16 flights daily along three basic commuter routes, has been affected by the strike on only one route, Connell said.

Colgan's essential service route, between Washington National Airport and Hot Springs, Va. (site of The Homestead, a resort and convention center), has been "greatly affected," said Connell, because it is "greatly dependent on connecting flights" of the major airlines.

Colgan's point-to-point route from Manassas to Dulles to Binghamton, N.Y., and its commuter route from Washington National to Asbury Park, N.J., -- operated mainly for business and Defense Department travelers -- have not been significantly affected by the strike, Connell said.

The setback experienced by some commuter airlines is only temporary, industry officials said. They are confident that rapid growth will resume shortly, after the Federal Aviation Administration enacts a system next month to stabilize airport traffic in the aftermath of the strike.

"Overall, the commuter industry, with reasonable financing and outstanding management, has tremendous potential for expansion," Connell said. "The big airlines are getting too expensive, and somebody's got to fill that gap."