Fairfax County's supervisors, citing long hours on the job and poor pay for their labors, voted unanimously yesterday to hold a public hearing April 9 on hefty salary increases for board members.

A proposal by retiring Supervisor Alan Magazine (D-Mason) would increase the part-time board members' salaries by 47 percent, from $15,000 to $22,000, and the chairman's pay by 66 percent, from $15,000 to $25,000.

The supervisors' last pay raise was four years ago, when salaries were increased from $10,000 to $15,000. "We're earning about 50 to 60 cents an hour," said Supervisor John Shacochis (R-Dranesville), who said he had been at meetings every night for the last three weeks. "Some board members put in 60 to 80 hours per week."

If salaries rose to the proposed level, the Fairfax board still would be only the fourth highest paid governing body in the Washington area. Elevted officials in Montogomery and Prince George's counties and the District of Columbia receive more.

The Fairfax proposal would apply to incoming board members, to be elected in November.

The proplosed measure immediately drew opposition from county employes, who are esxpected to receive a 5 percent pay increase in next year's budget.

"I think it's outrageous," said Pete Moralis, director of the Virginia chapter of the American Federation of State County and Municipal Employees, whose members include 3,000 county blue collar workers. "It seems rather strange that they (board members) voluntarily follow the president's guidelines in terms of employes' salaries. But not when they're talking about their salaries."

Even though county employes have received pay increases annually, he said, those increases "didn't keep pace with the double-digit inflation."

Moralis said it was "ironic" that Magazine, who is not seeking reelection, would introduce the measure. Magazine said yesterday in an interview that he introduced the measure because, "It's easier for me since I'm not running." He said it would place "a politicial liability" on his colleagues who are seeking reelection if they initiated the pay increase.

Supervisor Audrey Moore (D-Anmandale) said Magazine's proposed increase was "too much.We're talking beyond what we should consider during inflation times."

She Proposed an increase from $15,000 to $18,000, but that measure failed for lack of a second.

The county's federation of civic associations, the largest citizens group in the country, already has endorsed the proposed pay increases, according to Carl Ericson, chairman of the group.

Ericson, who plans to speak at the April 9 hearing, said, "The predominant feeling (among the association members) is that the responsibility of running the county demands the kind of salary that will attract a high caliber of people and hold them."

He said the association was disappointed that Magazine and Supervisor Warren Cikins (D-Mount Vernon) were not seeking reelection. Ericson blamed the strain of trying to carry out the responsibilities of a supervisor as well as holding down a full-time job as reasons that led the two to decide to retire.

The salaries for chairman and council or board members in other area jurisdictions are $28,500 and $26,000 in Montgomery; $24,619 and $22,119 in Prince George's $10,000 and $9,000 in Arlington, and $8,200 and $7,500 in Alexandria.

The D.C City Council recently raised salaries for its newly sworn members to $37,000. Incumbent members continue to receive $30,000,but that figure will increase to $37,000 in 1981. The chairman, the council's only full-time official is paid $47,000.