Loudoun County's "no-growth" policy has failed so miserably that county officials are preparing to scrap it in favor of "managed growth" that could bring a dramatic 66.7 percent jump in Loudoun's population by 1990.

Since 1972 the county board, trying to hold onto Loudoun's agricultural-rural character despite the relentless westward push of the Washington suburbs has refused to approve any rezoning applications.

Suburbs kept replacing farms, anyway. From 1970 to this year, Loudoun's population grew a whopping 76.5 percent from 34,000 to 60,000, one of the sharpest growth rates in the Washington area.

Furthermore, court-ordered rezonings and out-of-court settlements have set the stage for 8,000 to 10,000 more houses - or as many as 30,000 more people.

"'No growth' has been a failure," said the county's new planning director, John Dugan.

"It postponed the impact, but it didn't stop it from happening."

"We can't put up a chain-link fence at the Fairfax-Loudoun line and keep everybody out. Growth is inevitable," said Carl. F. Henrickson, chairman of the Loudoun County Board of Supervisors. He said the new managed growth plan 'is the recognition we can bring in growth on our own terms, not the courts' or the developers'".

By 1990, Dugan said, Leesburg Pike (Rte. 7), Loudoun's main corridor to the central urban area of metropolitan Washington, could be choked with 100,000 cars a day. Traffic of that magnitude - the road now handles about 18,000 cars a day - could cause 17-mile-long commuter-hour backups from Tysons Corner in Fairfax County to Leesburg, the Loudoun County seat.

To head off that and other spectres of too-rapid unbuanization, Dugan and his planning department have drawn up a new master plan that, they hope, can make future growth manageable. The plan was presented to the supervisors yesterday.

The new plan, which will go to public hearing next month, would not attempt to erect a legislative wall against development - the intention of the unsuccessful no-growth policy.

In essence, the "resource management plan," as the new policy is called, would try to spread out growth so it would not overwhelm roads, schools and other public facilities.

The conventional wisdom is that managed growth will not work in Virginia because the courts supposedly are too sympathetic to land owners - a tradition, the story goes, that is tied to the historical fact that the state's wealth derived more from the land

Fairfax often is cited as an example of the alleged judicial tilt toward land owners. Several years ago, Fairfax, when it was in the midst of drawing a new comprehensive plan, rejected two rezonings for suburban development, claiming that public facilities were inadequate. The courts reversed the supervisors.

Loudoun planning director Dugan said Fairfax failed because rejection of the rezonings was discriminatory to the landlords. "We're assuming, on the bottom line, that all zoning decisions have to be made with land owners' rights in mind."

Instead of telling a developer he cannot build what he wants to, Loudoun, under its new plan, would tell him to phase the growth according to a schedule determined by public facilities - those in place and those planned.

In addition, Dugan said, the county would not single out one developer - what Fairfax did in each of the two crucial cases it lost in Virginia courts - but apply the same rules to all potential development in each of the county would be divided under the resource plan.

To strength the county's hand if any disputes are taken to court by developers, the resource plan will contain a detailed inventory of the county's public facilities - how much sewer and water capacity is left, the level of traffic on nearby and corridor roads - and what impact new growth would have on county spending if more facilities were required.

In Fairfax, the center of growth in metropolitan Washington, the phasing of development has virtually been left up to the developers themselves, even though the master plan sets targets (up to 1990) in the districts into which the county is divided.

One recent result has been an explosion of new housing in the Burke area of southwest Fairfax that has overwhelmed roads and forced the long-distance busing of public-school students.

Dugan estimates that while managed growth could push Loudoun's population to 100,000 by 1990, continued court intervention in rezoning cases could push the population to 120,000 by that time.

To ease congestion on Rte. 7, the resource plan calls for a bypass that would run to the north and extend into Fairfax, connecting with the Springfield bypass, which is scheduled to be built in the 1980s from the Herndon-Reston are a to last Rte. 7.

According to Dugan, the county, now has sewage capacity for 4,000 to 5,000 additional houses. "It might be nip-and-tuck by 1983 or 1984," he said. One solution, he said, would be for Loudoun to buy capacity in a Fairfax County sewer project that will divert sewage from the Herndon-Reston area (near Loudoun) to the spacious lower Potomac Treatment plant.