The future of a vast area west of Dulles International Airport was being hashed out yesterday in a flurry of phone calls and public exchanges, as competing groups of Loudoun County supervisors sought enough votes to pass new development regulations.

Elected officials in Loudoun, which has grown faster than any other U.S. county since 2000, were eyeing Supervisor Jim Clem (R) -- a low-key and occasionally sharp-tongued former Leesburg mayor and funeral director -- as a key swing vote on a Board of Supervisors that is closely divided on how to govern 300 square miles of semirural land.

At issue is how the county should respond to a Virginia Supreme Court ruling in March that threw out strict building limits, which were passed in 2003 after three years of planning debates and political posturing. Most board members have said they want to replace the county's decades-old zoning rules, which were restored by a local judge after the Supreme Court ruling and which require three acres per home.

But attempts to fashion a replacement have sharpened a long-running debate in Loudoun on the future of suburban growth and rural business, housing affordability, property rights and the environment.

At a public debate last night that included feverish lobbying by real estate industry representatives and bouts of angry rhetoric -- and a strategically timed break when it appeared one group was going to lose a key vote -- a majority of supervisors voted to move ahead with two plans rather than decide on one.

Clem and Supervisor James Burton (I-Blue Ridge), architect of the invalidated 2003 rules, offered a bipartisan compromise plan ahead of yesterday's debate. That compromise combined elements of plans offered last month by Supervisors Lori Waters (R-Broad Run) and Sarah R. Kurtz (D-Catoctin).

In hectic discussions that continued in the hours before yesterday's board session, Supervisor Bruce E. Tulloch (R-Potomac) said he called Clem to seek support for an alternate plan -- which Tulloch and Supervisor Mick Staton Jr. (R-Sugarland Run) were advancing -- that would allow more building.

Last night, five supervisors on the nine-member body, including Clem, voted in a nonbinding straw vote against formally considering Tulloch and Staton's plan. But before the board voted on the Clem-Burton proposal, Tulloch called a break, which he later acknowledged was a stalling tactic.

"I can see the fix is in and that's okay. I can count to five," Tulloch said.

But after the break, Supervisor Stephen J. Snow (R-Dulles) called for both proposals to be sent forward to the board's June 21 meeting for formal debate. That motion passed with five votes, including Clem's.

"I think they both should be out there for people to view," Clem said, adding that he was leaning toward the Clem-Burton proposal, perhaps with modifications.

The 2003 building limits, thrown out on a technicality, required 20 acres to build a home in northwestern Loudoun, or 10 acres per home if the homes were in a cluster.

The rules required 50 acres to build a home in southwestern Loudoun, home to Middleburg, the hunt-country tourist draw, and numerous large estates and land holdings. Many of those are in permanent conservation arrangements that prevent further development.

The three-acre zoning, now back in place, theoretically would allow the construction of 46,000 more homes in the western two-thirds of Loudoun, according to the latest county analysis. A separate county calculation found that three-acre zoning might allow 37,000 more homes. If the county reinstated the 2003 rules, 10,000 homes could be built, according to county officials.

Compared with the 2003 rules, the plan offered by Clem and Burton would make it easier for landowners to carve up, and sell off, parcels. Property owners could cut off building lots at will, though some parcels would have to be large enough to support agricultural enterprises, according to the proposal.

Under that plan, owners with parcels of 20 acres or more in northwestern Loudoun could build a home on every 10 acres. Owners in southwestern Loudoun with 40 acres or more could build a home every 20 acres.

Following an idea offered by Waters, landowners would be allowed to build one home every 71/2 acres in the northwest, and every 15 acres in the southwest, if they applied for permission from the county board and paid for transportation improvements. Tulloch and Staton pushed a proposal that would allow clusters of five acres per home in northwestern Loudoun and 10 acres per home in southwestern Loudoun.