The Justice Department yesterday indicated that it is concerned about agreements among AT&T and other telephone companies to divide among themselves half of the future market for new mobile telephones.

The Justice Department's concern was expressed to the FCC, which is considering applications from telephone companies and from other companies in the communications and electronics fields to set up the new mobile phone services in the nation's major cities.

The technology is called cellular radio because a city is divided into sectors, or cells, and low-power radio messages are passed between those cells.

Hundreds of firms have responded to the FCC's invitation for franchise applications. The FCC has divided the market in two -- in each city it plans to approve a telephone company franchise and a competing one operated by a firm not in the telephone business.

The FCC has invited competing firms to form joint ventures to speed the approval process, and that process is beginning. Yesterday, the Justice Department said this action could raise "serious questions under the antitrust laws."

The Department urged the commission to clarify its position before granting applications, noting that such clarifications would facilitate the department's review of the issues raised.