When Mobil Oil employes were sent to scout out territory for a new office building near Washington several years ago their search was more like a spy operation than a corporate real estate search.

They used fictitious names and worked through intermediaries so that their identities could remain secret. It took the county 18 months to figure out who they were according to Fairfaxz County officials. "Sometimes they'd come in and not use any name at all," said David Edwards, director of the Fairfax County Economic Development Authority.

Mobil slipped up, however, when one employe called his colleague by two different names during the same meeting, Edwards said.

Many companies looking for greener opportunities often color their activities with anonymity until the deal is finally closed. Such is the case with 1, 460 acres of land called Fairfax West, which is touted as one of the county's newest hot properties. Landowners and rumormongers say that an oil company, a retail store and another national firm are seeking locations there in the Rte. 50, Interstate Rte. 66 corridor.

But the owners, county officials and others connected with the land refused to name what companies are interested. It was learned, however, that Montgomery Ward is looking at the property as well as other sites in the Washington area for a retail store.

"I'm sworn to secrecy," said Jack W. Carney, head of a group of landowners who banded together in 1964 to get the land sewered. They finally did it last year at a cost of $3.1 million, Carney said.

"We're looking at the area, but we haven't committed ourselves to anything," a Montgomery Ward spokesman in Baltimore said. "We're looking to expand our market in the Washington area."

The spokesman said that many companies like to keep such plans secret, but Wards had not committed itself to anything."As soon as it becomes apparent a Wards (or other store) is interested in building there, there's a tendency for people to jack up prices on you."

The spokesman said that when a developer several years ago was buying up land for his project "he had different people going in and buying up land in different names. Until the papers are signed and they're digging a hole, nobody wants to talk about it."

Until last year when bids went out on sewering the land, which will be anchored by the new Fair Oaks Mall, few people were interested in the property, Carney said. Now, depending on the land use and zoning, the land per acre could sell for $30,000 to $200,000, Carney said.

The Fairfax County government is expected to relocate its offices on a $5.5 million, 266-acre site called the Smith-Carney property.

The Fair Oaks Mall, a mammoth 137-acre shopping center, is scheduled to contain 125 stores and open next year. Woodward & Lothrop will be one of the major stores there.

The landowners and the county are working hard to bring in industry to the land, valued at more than $100 million.

"There's a lot of interest in that area by a variety of companies," including an international hotel chain, said Robert Torgerson of the county economic development authority. But Edwards said that companies take many years to decide on a piece of property. "We don't have anyone on the immediate horizon who will make an announcement" about locating there "in the next few months."

Edwards said his office hopes to locate an office park on the property, "a clustering of people," If the county locates its headquarters there, certain governmental support servies such as data processing or printing companies would find the site attractive, said Keith Taylor, another authority official.

Even if several companies do decide on the area, the drowsy, mostly wooded area in the center of the county would see little change for many years. The government center alone is expected to transform the area to an employment and commercial hub attracting more than 10,000 employes.