D.C. Del. Walter Fauntroy vowed yesterday to establish in the city's next budget a separate office of economic development, which was eliminated by Congress last year.

Acknowledging that the city faces budget problems, particularly with an impending shortfall, Fauntroy said that "a shortfall is going to be very difficult to handle" unless the economy becomes stronger. An improved economy could result from strong promotional efforts of a separate department of economic development, Fauntroy said.

Fauntroy, addressing a D.C. Chamber of Commerce luncheon, also took the opportunity to criticize President Carter's economic policies, and he blamed some of the city's problems on the President's budget and the Federal Reserve System.

Fauntroy, who has announced his support of presidential contender Sen. Edward M. Kenndy (D-Mass.), called Carter in a written statement "neither consistent, wise nor strong." Fauntroy said that statement was accidentally omitted from his actual spoken remarks.

He said that "attracting business and its associated support and functions will greatly improve the economic climate of this city so that the kinds of concerns you and I have read about in the paper concerning the fiscal strength of our city government will not be further exacerbated."

House and Senate conferees, who last year rejected the city's proposal for $665,000 for a separate economic development office, were afraid that such an effort would industrialize the city. Fauntroy said there are moves to ask for $100,000 for such an office in the 1981 budget, but he said that $600,000 is necessary.