Mobil Corp., parent company of the nation's third largest petroleum firm and of Montgomery Ward & Co., a large mass retailer, is considering relocation of its corporate headquarters from Manhattan to Falls Church.

Last year, Mobil announced plans to move its 800-employee domestic marketing and refining division to a 185-acre site in the Virginia suburbs of Washington, provided zoning changes are approved.

Now, according to Mobil chairman Rawleigh Warner Jr., his company is studying the possibility of moving nearly all of its 2,700-person corporate staff here. A decision will be made in the next six months and if Mobil does move here a minimum of 200 to 300 people would remain in New York, Warner told reporters of The New York Times on Monday.

A Mobil spokesman said yesterday that Warner's comments should be considered as a natural consequence of the company's earlier announced policy to "review the efficiency of all locations" and not an indication of a change in direction.

Officials of New York City, faced with an economic drain caused by decisions of many firms to relocate offices elsewhere, are urging Mobil to remain.

Warner quoted a survey of Mobil employees that found 80 per cent willing to work "any place but New York. We cannot get younger people who are really going to move up in the company to come to New York City."

The Mobil spokesman said yesterday that Warner was referring to anattitude survey of managerial and professional people around the country, who were asked about moving to New York for a promotion and higher salary. The spokesman emphasized that a survey had not been conducted among the 2,700 workers in Manhattan. At least some of the New Yorkers have no desire to leave, he added.

Warner said the suburban Virginia location was being studied by Mobil because of the absence of big city problems, for the most part: proximity to federal government of Dulles International Airport as a transportation hub.

Speaking of the federal government, Warner was quoted as saying "Our problems emanate from Washington D.C. . . . we spend a lot of time there now, being there would put us in constant contact with them."

The land being studied by Mobil for its headquarters is a 185-acre plot bounded by the Beltway, Route 50 and Gallows Road, which belongs to the estate of Earl N. Chiles. A Fairfax County task force of citizens, land owners and planners has been studying proposals to rezone the land for commercial use.

If Mobil moves here it would become the largest corporation based in metropolitan Washington and its large staff would make it one of the area's major private employers. Last year, Mobil revenues totaled $27.7 billion compared will $22.4 billion in 1975.

In terms of annual sales, the largest company based here now is the $1.2 billion Martin Marietta Corp., a diversified aerospace and construction materials firm.