Arlington County Republicans, who came under sharp attack a year ago for replacing the only black on the county school board, yesterday named a black community leader to the school panel.

The appointments of Evelyn Reid Syphax, a member of one of Arlington's oldest black families, and Claude M. Hilton, a former county prosecutor, will for the first time in 25 years place the five-member school board under the control of Republicans appointees.

County Board chairman Walter L. Frankland Jr. and his fellow Republican board members have for the past two years quarreled bitterly with the Democratic-dominated school board. Frankland has blamed Arlington's educational problems and an alleged decline in the schools on the school board and the "inner-city educational philosophies" of Superintendent Larry Cuban.

Hilton and Syphax, who could not be reached for comment yesterday, will replace outgoing board member Mary Margaret Whipple and Richard A. Barton on July 1.

When Frankland announced last year that he planned to end an eight-year tradition of having a black school board member by replacing Dr. Thomas Penn, he told a reporter that "with a black on the board for the past eight years Arlington's school system has gone down."

That statement angered many blacks who account for more than 14 percent of the Arlington school population. They were also angered by the fact that O. U. Johansen, a former high school principal removed from his job for alleged incompetence and inability to deal with minority students, was hand-picked by Frankland to be Penn's replacement.

Frankland, who has rejected charges he is insensitive to the county's blacks, yesterday downplayed the significance of picking a black, with ties to the Democratic Party for the board. "I don't think (party affiliation) is material," Frankland said. "The appointees will be in keeping with the majority of the (county) board."

But when Board Member John W. Purdy, a Democrat, commended Barton and Whipple for "their outstanding service in the face of repeated abuse by the chairman" Frankland scowled.

"That's the most ridiculous statement I ever heard," snapped Frankland. He charged that when Purdy was county board chairman "the direction of the school board led to complete political upheaval in Arlington."

School board chairman Ann C. Broder, a Democrat whose term expires next year said yesterday she welcomes both appointees. "Even though Mr. Hilton doesn't have a lot of background in education he'll learn," said Broder. "Mrs. Syphax is a wonderful choice and I'm glad to have a representative of the black community on the board again."

In other action the board adopted a $19.5 million utility budget which will boost the average water and sewer bill of homeowners about $45 annually.

The budget, which is 33 percent higher than last year, means that the average Arlington homeowner will pay $172 during the next year. The same amount of water and sewer service previously cost $127.

Officials said the increase, which is effective immediately will boost the cost of 1,000 gallons of water from $1.59 to $2. The increase was needed to meet increased operating costs for a sewage treatment plant in South Arlington, officials said.