The Fairfax County Chamber of Commerce will recommend this week that the annual salaries of the county supervisors be increased by at least $13,500 -- to $35,000 -- soon after the 1987 election and then raised to $45,000 by 1992, according to chamber and county officials.

The nine part-time supervisors now make $21,589 a year, a salary that chamber members have called "woefully inadequate."

The chamber, which took up the controversial issue last month, also will recommend that the supervisors retain their part-time status, rejecting suggestions that Fairfax switch to a full-time board.

Chamber officials have scheduled a Wednesday afternoon news conference to reveal their findings, which then will be passed on to the Board of Supervisors for a vote. William F. Blocher, who chaired the chamber's pay raise committee, said yesterday that he would have no comment on the matter until Wednesday. However, a number of chamber and county officials familiar with the proposal agreed to discuss it on the condition that they not be identified.

According to those sources, the chamber committee concluded that the supervisors were far underpaid and that a substantial pay raise was needed to bring their salaries more in line with those of elected officials in Montgomery County, Prince George's County and the District.

The Fairfax supervisors make $15,000 less than the officials in Montgomery County and $25,000 less than those in the District. Like the Fairfax officials, the council members in those jurisdictions are part-time. The council members in Prince George's County, where the population is far less than that of Fairfax, earn $10,000 more than the Fairfax supervisors.

The issue of parity, which helped fuel the chamber study, has been a source of contention on the Fairfax board for some time. Several supervisors have complained they are underpaid compared with their counterparts elsewhere.

Supervisor James M. Scott (D-Providence), one of the most outspoken advocates of a large pay raise, said when informed of the chamber's recommendation that it did not go far enough. "It's certainly better than what it is now, but it would still fall far short of what the other major jurisdictions in the area" are paying, he said.

Supervisor T. Farrell Egge (R-Mount Vernon) also was less than enthusiastic about the pay proposal. Saying he was "a little disappointed in it," Egge said the proposal's effectiveness can be better measured during the 1987 county elections.

"I think we'll know whether it goes far enough when we see whether people who have not had competition in the past get competition this time around," Egge said. "We have disenfranchised a large segment of our population from running for office because they just cannot afford it."

Board Chairman John F. Herrity said he was opposed to the chamber proposal because it went too far. Herrity called the recommended pay scale "an outrage."

Since under county law supervisors cannot grant themselves a pay raise, the new salaries would not take effect until the new board takes office in January 1988.