Xerox Corp. announced plans yesterday for an $8 billion to $10 billion commercial and residential development on a sprawling tract of wooded land it owns 30 miles northwest of the District off Rte. 7. The Loudoun County project, if approved and undertaken, would be one of the largest developments in Northern Virginia.

The Xerox International Training Center already is located on the 2,267-acre tract about 10 miles north of Dulles International Airport. Although plans have not yet been submitted and details are not final, the development also would include:

* As many as 20 separate corporate headquarters;

* About 1,800 upscale homes, including single-family houses and town houses with prices starting at about $150,000;

* A large resort hotel with major recreational facilities and a conference center, and a large commercial hotel.

The Xerox project is one of 11 new or proposed developments representing a growth boom covering more than 5,000 acres in eastern Loudoun County.

Construction on the Xerox development probably could not begin until early 1986 and the project would take at least 10 years to complete, officials said.

The development, which is so far unnamed, would provide more than 10,000 jobs, according to Xerox officials. They said the project would be financed in large part by private developers, but that Xerox would maintain ultimate control over all design plans.

Loudoun County officials, who must approve zoning changes if the project is to proceed, expressed uniform support for the plan, but noted that they expect Xerox to make major improvements to roads leading to the site, particularlyRte. 7.

"I'm almost ecstatic about it," said County Board Chairman Frank Raflo. "If it was any better I couldn't stand it."

Among the new projects in the county are a shopping mall known as the Lerner project, proposed for the intersection of Rte. 7 and Rte. 28, and a large residential project called Ashburn Village to be located south of Rte. 7 just east of Leesburg.

In addition, just 10 miles south of the Xerox site is the 35-acre tract planned for the Center for Innovative Technology, a state-supported complex to coordinate corporate use of university research, which is expected to attract heavy commercial development to the area.

Xerox officials said yesterday their project would be the largest ever undertaken by the company's real estate arm, Xerox Realty Corp.

Xerox officials said they have not yet contracted with a developer, nor do they know what corporations will occupy the commercial buildings.

"A lot of people will come to us," said Thomas C. Abbott, manager for media relations of the Stamford, Conn.-based firm. "We won't have to beat the bush for them."

Abbott stressed that the project will be "a high-quality, high-cost development," with about 1,000 acres of landscaping threaded among the building sites.

He said there would be no effort to provide housing for middle- or lower-income residents.

Loudoun County officials said they expect no major hitches in approving the Xerox plan. The company, the largest taxpayer in the county, has built up considerable good will in Loudoun, which badly needs commercial development. Xerox has operated its training center off Rte. 7 since 1974.

Xerox officials have been briefing top county officials on the project for the past six months or so. Abbott said reaction to the proposed development has been positive.

"I think it's tremendous," said Supervisor Steve W. Stockman. "I think it's very exciting."

"I can't imagine that there would be significant opposition," said Raflo.

Most county officials contacted yesterday said they were confident that Xerox would make major improvements to Rte. 7 in order to handle the traffic generated by the project.

Abbott said the company has hired a consulting firm to study the project's impact on traffic.

"This would be the first time we would see fairly major traffic going west toward Xerox and Leesburg in the morning," said Ann B. Kavanagh, the county supervisor who represents the area that includes the Xerox site.

Abbott said Xerox plans to submit the project to the county for review next week.

County officials said it would take at least six months for the project to be reviewed and the property rezoned. The Xerox land is now zoned for agricultural use, and company officials said they will seek zoning that would allow a planned residential community, as well as corporate, research and development and retail facilities.