The Fairfax Hospital Association, just weeks after it helped defeat plans for a private, 200-bed hospital in Reston, is seeking permission to open a heart surgery unit at one of its hospitals and add 60 beds to another.

The nonprofit hospital association has proposed spending $4 million to add the new beds to the 656-bed Fairfax Hospital near Rte. 50 and to establish a heart surgery unit at the underutilized Mount Vernon Hospital it owns off Rte. 1 in Hybla Valley.

"We know for a fact we can fill every one of those beds," said George Warnenhoven, assistant planning director for the association. He said that the proposals, currently before the Northern Virginia Health Systems Agency, will not increase health care costs in the county.

Supporters of Humana Inc., a Louisville, Ky., profit-making hospital chain whose controversial proposal for a hospital near Reston was rejected this winter, criticized the association for seeking additional hospital beds after arguing that Humana's proposal was unneeded.

"Their proposal would not bring one of those beds any closer physically to the more than 100,000 who live within five miles of my home at Reston," said Karl Ingerbritsen, who heads a citizens group that supports Humana. He said his group would "be as vigorous as we can in opposing the expansion of beds at Fairfax Hospital."

George Barker, associate director of the local health systems agency echoed Ingerbritsen's remarks. "We're not too enamored of the proposal. . . "he said.

Agency officials said they plan to hold public hearings on the association's proposal later this month. It must be approved by both the agency and the Virginia state health commissioner before the association can proceed.