We studied the 1s2s nl and quartet states of the lithium atom by a model-potential method with B-spline basis functions in the CI scheme. The transition wavelengths and probabilities, and lifetimes for electric dipole decay are calculated and compared with experimental and other theoretical results. A large number of transitions, which can possibly be observed, are presented. Our calculated transition wavelengths and lifetimes are in good agreement with the available experimental results. Including relativistic, radiative, and mass-polarization corrections for 1s2p and 1s2s cores, we calculated for - transitions. Some of these agreed with experimental results within 1 Å. The lifetime of [1s2p3s] is calculated to be 9.89 ns, which is the best agreement with the experimental result, ns, among the present theoretical results. The lifetime of [1s2s3s] is also improved.