WASHINGTON — The number of retail food establishments exempt from a requirement to register with the Food and Drug Administration under the Food Safety and Modernization Act would increase under a proposed rule from the F.D.A. Currently, food facilities that manufacture/process, pack or hold food for U.S. consumption must register with the F.D.A. Retail food establishments are exempt. The proposed rule, found in the April 9 issue of the Federal Register, would clarify the definition of “retail food establishment” to include such direct sales platforms as roadside stands, farmers’ markets and Community Supported Agriculture (C.S.A.) programs. The F.D.A. will accept public comments on the proposed rule until June 8. The F.D.A. estimated about 71,000 farms only sell food products to consumers in ways that include farmers markets, roadside stands and C.S.A. programs. The F.D.A. does not know how many of these farms currently must register with the F.D.A. and, under the proposed rule, no longer would be required to do so.