Sherry Johnston, manager of Suburban Florist in Bethesda, ordered more miniature American flags and red, white and blue bows than she needed for Fourth of July sales. Now she is looking like a business genius, as calls flow in from across the country from well-wishers wanting to send patriotic flower arrangements to President Reagan.

Reagan, recovering from surgery at Bethesda Naval Hospital, is receiving hundreds of arrangements and bouquets daily, according to White House spokesman Dale Petroskey. At Suburban Florist and Bethesda Florist, both less than a mile away, business is bustling.

Bob Callahan, manager of Bethesda Florist, said his shop is getting about 25 calls a day for flowers for the president, including orders from government officials and foreign diplomats. Callahan has sent everything from a single rose to $250 arrangements of violets and birds of paradise.

Callahan said he believes the flowers are cheering the president, as are accompanying messages such as "Fight, man, fight. The country needs you," or "Our prayers are with you."

In a White House statement issued Tuesday, Reagan called the outpouring of flowers, balloons, candy and telegrams "the best medicine I can have."

At the front of the Suburban shop yesterday, an arrangement ready for delivery included blue alliums, red carnations and white spider mums and pompons resembling fireworks. In the center was a 6-by-10-inch American flag. Also on its way to Reagan was a bouquet of a dozen red roses decorated with three small plastic flags.

Suburban manager Johnston said the patriotic ornaments have come in handy in arrangements, but she's running out of them.

She takes pride in arranging flowers for the president and said the shop has been averaging about six such orders a day, most from out of state.

"Is he really getting any of these? . . . I try to be creative with each one because you think maybe he's only getting a few of them and this will be the one he sees," she said.

Petroskey said the president is seeing all the flowers, but only after they pass Secret Service inspection.

Sherry's sister, Susie Johnston, who delivers the Suburban Florist's flowers to the hospital, worried good-naturedly about the manhandling she said the flowers are getting from Secret Service agents.

"These men take the stuff out and stick little probes in and they have earphones in," Johnston said.

Secret Service spokesman Robert Snow said officers are not disrupting the arrangements.

Flowers that don't fit in the president's room are being distributed to other parts of the hospital. On Tuesday, First Lady Nancy Reagan went to the pediatric ward and gave children flowers and balloons.