Arlington County Board Chairman Dorothy T. Grotos and Vice Chairman Walter L. Frankland Jr. last night were endorsed by the Arlington Reelected to second four-year terms on the County Board.

Grotos and Frankland, both independents, will face Mary Margaret Whipple, the school board chairman, and Charles Rinker, president of the Arlington Housing Corp., in a November election that will determine whether Republican backed candidates will retain majority control of the county board. Last month Whipple and Rinker, who are running as independents, received the joint endorsement of the Arlington Democratic Party and the Arlingtonians for a Better County organization.

"We have tried very hard over the past 3 1/2 years to move the county forward," Grotos told 600 persons who crowded into the Lyon Village Community Center last night. "We want to prevent a return to the philosophy of tax and tax, spend and spend," said Grotos.

Henry Hudson, a former member of the Young Democrats, received the party's endorsement for commonwealth's attorney. Hudson will face the winner of a June 12 Democratic primary that will pit incumbent prosecutor William S. Burroughs Jr. against Democratic-backed county board member John W. Purdy.

Also endorsed at last night's mass meeting was Charles Bonneville, who defeated Roxy Crack and Fred Bridgeman in his bid for GOP backing to become Arlington's sheriff. Bonneville will face Democrat James Gondles in the November election.