Résumé : The reaction e+p → e+X is studied with the H1 detector at HERA. The data cover momentum transfers Q2 between 200 GeV2 and 30000 GeV2 and correspond to an integrated luminosity of 35.6pb-1. The differential cross section d dσ/dQ2 is compared to the Standard Model expectation for neutral current scattering and analysed to search for (ee)(qq) contact interactions. No evidence for new phenomena is observed. The results are used to set limits on scales within models of electron-quark compositeness, quark form factors and the exchange of virtual heavy leptoquarks. A search for gravitational effects mediated through the exchange of virtual gravitons which propagate into large extra dimensions is presented. (C) 2000 Elsevier Science B.V.