A majority of small businesses are experiencing revenue growth in 2012, but are still not planning to hire additional employees, according to a new survey from Constant Contact Inc., a Waltham-based provider of e-mail marketing services.

Only 11 percent of small businesses surveyed said that they expected their 2012 revenues to drop, while 59 percent said they expected revenues to increase, and 30 percent said that revenues would remain flat, the Constant Contact Spring 2012 Small Business Pulse Survey found.

Nevertheless, 66 percent of small businesses surveyed said that are not planning to hire additional full-time employees in the next six months.

While many small business owners are optimistic about revenue projections, the fact that they aren’t hiring and the fact that operating costs are rising suggest the mood is one of “cautious optimism,” Constant Contact chief executive Gail Goodman said in a statement.

Constant Contact said the survey was conducted in May. Participants were recruited from Constant Contact’s customer base. And survey results include feedback from 728 respondents across a range of industries.