The District's urban renewal agency yesterday gave city officials and developers of the Portal Site in Southwest Washington another three months to negotiate a sales price for the 10-acre parcel.

The extension of time was the fourth time in six months that the D.C. Redevelopment Land Agency has delayed its deadline for concluding negotiations with the team of developers who won the redevelopment rights in February 1982.

The agency's original deadline was September 1982.

Yesterday deputy mayor Ivanhoe Donaldson told the five-member RLA board that the two major stumbling blocks to the negotiations were discussions with Conrail for air rights over the railroad tracks that run through the site and the possible relocation of a GSA coal bin that abuts the development area. The resolution of both of these issues could affect the price the group will pay the city for the land.

These were the same two issues cited last September as the reason for failure to meet that first deadline.

Donaldson also reported that agreement appeared near on Metro Center, another major city project that has been stalled for years. But he said some issues must be resolved between the developers and Hecht's department store before a final agreement will be reached. A new Hecht's store is the first phase of the project.