Generation of low frequency electromagnetic solitons in plasmas near the critical density by use of an ultrashort intense laser pulse has been studied with a two-dimensional (2D) particle-in-cell simulation code. They are formed while the ultrashort laser pulse is exciting a wake field, with its trailing edge experiencing strong frequency down-shift and part of its energy trapped in the plasmas. The formed solitons are usually found to move with small velocity, which results in the formation of plasma cavities and the acceleration of ions to high energy. It is also found that the soliton formation in 2D simulation geometry depends heavily on the polarization state of the incident pulse.