A mini-boom in the value of land on the fringes of metropolitan areas may be gathering steam--opening the door to astute, small-scale investors, including those with little cash and modest incomes.

That's the opinion of real estate analysts in several parts of the country. They say three key economic factors have combined to produce the most significant opportunities for land investment since 1978:

* The housing rebound is moving faster than expected. Builders in areas such as Atlanta, San Antonio, Dallas, Chicago and Washington already are running out of finished lots suitable for the modest-priced, first-time-buyer units that they're selling fastest. Data collected by U.S. Housing Markets, published by Advance Mortgage Corp., indicate that developable land has doubled in value in some markets in the past year. In a number of markets, raw land is jumping by 1 to 2 percentage points a month.

* Land prices throughout the country dropped far more dramatically than any other form of real estate during the past three years. While housing prices stayed flat or dropped marginally during the past year, for instance, raw land values plummeted by as much as 20 percent, according to data from the U.S. Department of Agriculture. Prices in many areas still are sitting at bargain-basement levels.

* The increasing likelihood of a steady recovery for the nation's economy in the coming two years will mean higher demands for the land by industry, commercial businesses and developers well into the mid-1980s. That, in turn, will mean sharp increases in values for strategically located parcels.

The outlook for land investment "unquestionably is the most exciting we've seen in a long time," says Colby Sandlian of Wichita, Kan. Sandlian's firm develops mini-warehouses, buys and sells land, and invests in other forms of real estate across the country.

Sandlian is best known, though, for his nationwide lectures on "small-option syndicates"--a technique he advocates for land "control" and profit by groups of small-scale investors who each have $5,000 to $10,000 to put into real estate.

The concept works like this: When economic conditions are on the verge of pushing developable land prices higher--as they are now--small investors should research and pinpoint "the directions of development" in the outlying fringes of their local markets.

"Where must housing go next? That's the first crucial question to ask," Sandlian says. "What parcels are going to make strategic sense for the commercial services that have to follow housing: the gas stations, convenience stores, small shopping centers and the like?

"I'm talking about development that's two, three, four years down the road, but development that is highly predictable, even inevitable, if you study your area intelligently."

Having identified land parcels, farms or raw acreage that fit this mold, the small investors then should negotiate with current owners for contract terms that are as advantageous as possible.

A $200,000 piece of land, for example, might be available for 10 percent down in cash, with the seller holding a 10-year note on the balance at 10 to 12 percent interest. To hold the property prior to closing the deal, the investors might have to put up $5,000 to $10,000 in earnest money.

The investors' sales-contract offer should contain two special "option" clauses that Sandlian says he has used in dozens of acquisitions. The first clause requires forfeiture of the earnest money "if for any reason the sale does not close" within a specified period.

The second clause allows the purchasers to pay another non-refundable $5,000 or $10,000 in cash later in exchange for the right to delay the closing by up to 12 months.

Stripped to its essentials, Sandlian's "sales contract" is actually an option arrangement. It permits purchasers to leverage their investment dollars: they use very little money to gain effective control of large chunks of property with high potential for appreciation.

The technique allows small groups of investors (perhaps guided by a knowledgeable local broker) to create partnerships that invest in multiple parcels of strategically located land, rather than banking on just one. Because less cash has to go into each parcel to control it for a year or two, a small partnership (syndicate) could readily gain rights to five or six pieces of land.

As successive option expiration dates arrive, the partnership either closes on each parcel and sells immediately to a developer, producing sizable capital gains, or agrees to acquire and hold the land for longer periods, using the favorable financing negotiated in the original contracts.

Land sellers--particularly those who need to get cash out of their property immediately--"are often very receptive" to land contract-option arrangements, says Sandlian. The sellers feel they can't lose when they have option money in hand and retain legal title to their property. The buyers, meanwhile, get the legal right to own that same property on favorable terms whenever they want, but they don't have to put up huge amounts of cash.

"It's a win-win situation," says Sandlian, "provided you've done your homework.