Plans to build a $320 million office park just outside Rockville have evolved into a bitter land battle between the city and Montgomery County that is threatening their normally harmonious relationship.

At the heart of the controversy is a choice 49-acre parcel immediately north of Montrose Road along I-270. It is an area that Rockville officials have long considered annexing, but for now remains under county jurisdiction.

In April 1985, a development firm approached Rockville with plans for Fortune Parc, a 1.7-million-square-foot hotel, office and retail complex. The developers asked the city to change the zoning to allow a development of that sort on the land with the assumption that the city would then annex the property. But, by June 1986, with the city failing to make progress on the zoning changes sought by the Fortune Parc Development Corp., the Arlington-based firm turned to the county in filing for permission to build on the site.

William E. Hanna Jr., a member of the County Council and a former mayor of Rockville, said the city "blew it with Fortune Parc."

"The city took too long and the developers came to us," said Hanna, chairman of the council committee that will consider the development. "I have some sympathy with the city over their desire to extend their borders, but in this case, they wasted their time and it's our turn."

Rockville Mayor Steven Van Grack, who voted alone in support of the requested zoning change, said he, too, believed the city "erred" in failing to make progress on Fortune Parc. But he wants the city to get another chance at annexing the property.

"In short, we would get all the traffic, with none of the tax revenues, and it's right on our border," he said. "We deserve a shot at this."

In what has become a race between the city and the county, Rockville officials are trying to persuade the county to delay progress on the zoning approval for Fortune Parc -- tentatively scheduled for County Council action in October -- in favor of moving more quickly on an agreement allowing Rockville to annex several properties -- among them the Fortune Parc site.

If Montgomery approves the Fortune Parc project before it approves the proposed extension of Rockville's boundaries, annexation of the lucrative property by the city would become virtually impossible.

Van Grack said, "This is our chance, but the county is acting as if it's over. We thought we were talking constructively, but it's frustrating that now we don't seem able to convince them that an agreement between us would help more than a fight over a piece of land."

At stake for Rockville are both money -- estimates for tax revenue from the land range from $500,000 to $1 million -- and pride. For the county, an agreement to extend Rockville's boundaries could prevent the county from controlling development in some of the areas that are considered prime locations for expansion of Montgomery's research and development corridor.

And, with development the key issue facing Rockville in a hotly contested mayoral race this fall, Fortune Parc could turn out to be either a political brass ring or an embarrassing example of a missed opportunity.

David Murphy, director of development for Fortune Parc, said his firm decided to go to the city first because "we were aware of the city's desire to expand and even though it would cost us $1 million more in taxes, we thought we would have the wrath of the city upon us if we went to the county first, building so close to the city and all."

Murphy said, "Frankly, I think we spent enough time with the city . . . . They have a real hard time making up their minds."

Rockville City Council member Douglas Duncan, who is challenging Van Grack for mayor this fall, said he intends to bring up Fortune Parc as an election issue. Duncan, who along with the three other council members voted against the initial zoning change sought by Fortune Parc, has been trying to portray Van Grack as a "pro-development" mayor.

Shortly after the City Council failed to approve the zoning changes desired by Fortune Parc, talks between the city and the county began on an agreement that would allow Rockville to expand its borders to include the Fortune Parc property.

What has happened since is a complex series of maneuvers aimed at cementing the agreement between the county and the city, which would outline what Rockville can annex and the rights and responsibilities both parties would assume in such a contract.

Called the Maximum Expansion Limits Agreement, the contract would end nearly 25 years of speculation about the areas, said City Manager Richard V. Robinson. Robinson said the proposal includes, "in effect, a second boundary around parts of the approved Rockville city limits," designating areas the city could annex someday, called Maximum Expansion Limits. In all, the city officials say they eventually would like to annex more than 875 acres. County approval is needed for such an agreement.

Duncan said he is encouraging speedy passage of the expansion agreement, and said that although the city is faced with losing Fortune Parc, he still believes he voted correctly.

"What we would have had was a wholesale change of our zoning to accommodate more development," Duncan said. "I couldn't support that. You can't cater our zoning laws to every developer, and that's what the mayor tried to do there."

Van Grack said the zoning change would have "still allowed us to reject Fortune Parc, or any individual project, based on its merits. But what we have now, I fear, is a project on our doorstep with no way to control it. I think that vote would have allowed us that control and kept Fortune Parc from going elsewhere."

While the county's progress on the Fortune Parc case has moved along at a steady clip, the council appears reluctant to proceed with final action on the expansion agreement.

County hearing examiner Philip J. Tierney last month rejected a request by the city to delay county hearings on Fortune Parc until December.

The first of three hearings is scheduled for Sept. 28. Van Grack said a postponement would have given the city and county more time to work out the expansion limits agreement.