Fairfax County's supervisors have split with the semi-official association that governs the county's hospitals over the group's proposed $90 million budget for 1979 and its reluctance to furnish less expensive alternatives.

"I think it's about time the association established contact with the needs of the public in Fairfax County", said Board of Supervisors Chairman John F. Herrity. "They can no longer sit over there in their empire and do exactly what they please."

The hospital group, the Fairfax Hospital Association, runs four county-owned facilities - the 656-bed Fairfax Hospital, Mount Vernon Hospital (235 beds), Commonwealth Doctors (160 beds) and a 65-patient per day ambulatory care center called Access in Reston - all on a lease arrangement. Its yearly budget is reviewed, but cannot be vetoed, by the supervisors according to the lease.

The dispute arose last month after the supervisors, displeased with an 11 percent increase written into the 1979 budget proposal, asked for two alternative drafts, one for six percent and one for eight percent.

In a letter to the board, William C. Shreve, president of the FHA's trustees, branded such a reworking an "extra exercise in futility" and said it would "tax our staff." He said the drafts would require the approval of FHA's trustees.

"We shouldn't have to wait for a meeting of the trustees to get the information we are allowed," said Supervisor James N. Scott, "This isn't the first time we told them we needed more information to adequately study their budget.

Herrity responded at the board's regular meeting last Monday by appointing a three-supervisor committee, consisting of himself, Audrey Moore and Joseph Alexander, to meet with County Attorney F. Lee Ruck, acting County Executive J. Hamilton Lambert and association officers to discuss the impasse.

FHA executive vice president Franklin P. Iams yesterday agreed to meet with the group next Tuesday. The FHA trustees are scheduled to meet the next day.

The lease provides the supervisors 30 days to review and comment on the association's to furnish the supervisors with financial information "at such times as requested by the county."

Ruck said his preliminary opinion was that the association, by its reluctance, had violated the terms of the lease.

Scott, one of the superviosrs' representatives on the board of trustees, first requested the alternative budgets at the trustees' Oct. 25 meeting. The request was voted down. Provoked by the denial, the supervisors made another formal request Oct. 30.

Shreve, in his letter to Herrity Nov. 3, said "it was with the most stringent restraints that we were able to hold the anticipated increase to 11 percent, 2 percent below the 1977 increase of 13 percent."

He attributed the increase to inflation and increased demand for services.

Scott has noted that the 11 percent increase "is almost double President Carter's suggestion for a limit to hold down costs."

Hospital Association spokeswoman Peggy Pond said association officials would have no comment on the board action until they were formally notified this week of the special meeting.

But she said the hospital's response to the supervisors could not be interpreted as a refusal because Shreve offered to bring the matter before the trustees again at their regular meeting or at a special meeting.