Most large Middle Atlantic banks increased their prime rates yesterday in concert with money center institutions of New York and Chicago, or indicated that they would have to join the new 8 3/4 percent level by the middle of next week.

Bank officers surveyed were unanimous in forecasting additional interest rate hikes in future months. Area bankers gave a mixed picture of current loan demand however.

W. Wright Harrison, Chairman of Virginia National Bank and its holding company. Virginia National Bankshares, said he was "somewhat surprised" that the prime rate had been increased "again this soon" after it jumped to 8 1/2 percent on April 28.

In a telephone interview from Norfolk, where Virginia's largest bank is based. Harrison said he will study the situation over the weekend but said VNB had no choice but join the parade of higher prime rates, that charged to best corporate customers.

"We can't hold out long at 8 1/2 per cent because General Motors. Ford, General Electric would be in here seeking to activate lines (of credit). . . regional banks have to follow, we couldn't meet the demand," he stated.

He said VNB currently is experiencing strong consumer and corporate loan demand, and faced no requirement to raise its rates. "I'm terribly disappointed they (larger banks) couldn't hold out longer. . . I'm afraid we'll see a prime rate over 9 percent before it will restrain credit enough."

But Harrison praised Federal Reserve Board Chairman G. William Miller for leading a drive to increase rates. While there is "some danger" of a recession in the next year "this is the only way to slow down inflation. . . if we can level off at about 9 percent we may avoid any deep turnaround," Harrison added.

Carleton Steart, chairman of America Security Bank in Washington, said his bank raised the prime to 8 3/4 percent yesterday because of the "cost of funds" it must attract to make loans.

He said the D.C. bank is facing strong demand for personal, mortgage and construction loans but a "mediocre" corporate loans business. Stewart added that he expects the prime to peak before year's end, possibly as high as 9 1/2 percent.

Riggs National Bank Chairman Vincent Burke Jr. said the city's largest bank probably would increase its in the face of record loan demand. The loan volume of Riggs was $925 million on March 31 and since has climbed some $30 million, Burke added.

Maryland National Bank, the largest in Maryland, is expected to increase its prime rate to the 8 3/4 percent level next week, according to senior vice president William Daiger. He said loan demand had been good but not "strong."

According to the Federal Reserve Bank of Richmond, which includes D.C., Maryland and Virginia banks among its members loan volume at 27 large commercial banks in the Fifth District rose $70 million in the week ended June 7. Financial loans accounted for all the increase.

Regional demand deposits fell $423 million in the most recent week surveyed while the volume of certificates of deposit jumped more than $90 million.