Despite the increasing frankness with which Americans discuss sexuality, many people are still uncomfortable about the topic of menstruation. According to the findings in a new report, a significant number believe that it should not be discussed at the workplace or in social situations, with a quarter of them considering it unacceptable even with other family members at home.

For the study of attitudes toward menstruation, entitled ''The Tampax Report'' because it was conducted for the manufacturer of Tampax tampons, 1,034 people, including 211 aged 14 through 17, were interviewed by phone about their perceptions of and attitudes toward the menses. The sample was taken between April 4 and May 3 by Research and Forecasts, the research arm of Ruder & Finn, the publicrelations concern. It was designed to be representative of all age, ethnic, sex, education and economic components of the population.

Clearly, the female cycle is not a subject Americans discuss with much ease. Only 35 percent said that it was appropriate to talk about it at the office and even fewer, 33 percent, thought it fitting to mention in social situations. Restrictions are also applied to other ways of divulging the fact that a woman is having her period, such as complaining about cramps and leaving sanitary products in evidence.

More than a third of the respondents said that even at home women should conceal the fact that they are menstruating; 64 percent said they should conceal it at work and 68 percent in social situations. Eight percent of the sample said they believed women should avoid contact with others when menstruating; the report noted that although proportionately low, that number represents 14 million Americans. Myths Are 'Rampant'