The new contractor brought in to rescue Metro's troubled Green Line pledged last night to complete the rebuilding of sections of U and Seventh streets NW by May 1991, in time for the scheduled opening of the transit agency's first Green Line stations.

It was the first time since Metro fired the original contractor in May that officials have said when they hope to finish the street restoration along the first of three Green Line segments that run through the Seventh Street and 14th Street corridors in Northwest Washington.

Most of the below-ground work on the Shaw-Howard University and U Street-Cardozo stations has been completed and trains have been tested along the track. But the continuing disrepair of streets torn up during the construction has angered residents of the Shaw and Cardozo neighborhoods.

Once the streets and sidewalks are rebuilt and landscaping is added by June 1, the two stations can open. Officials said they would announce the date of the openings within a month. They originally were scheduled to open Dec. 1.

Robert J. Howard, a vice president of Perini Corp. of Framingham, Mass., told about 65 Shaw and Cardozo residents that a timetable worked out by the company and Metro officials calls for the rebuilding of Seventh Street from Rhode Island Avenue NW to U Street NW to begin Aug. 27 and end Nov. 12.

He said the restoration of U Street NW, from just west of Vermont Avenue NW to just east of 14th Street NW, would be done in three phases starting Aug. 16 and ending May 5, 1991. Sections of U Street will be closed to traffic during this work.

"It is a schedule I believe represents targets all of us are committed to meet," said Metro General Manager Carmen Turner. "We just apologize for the delay . . . but I do believe we've turned the corner."

Last night's meeting at the Watha T. Daniel Library at Eighth Street and Rhode Island Avenue NW was an attempt by top Perini and Metro officials to pacify residents who have put up with more than two years of disruption.

For the most part, community leaders and residents said they were willing to go along with Metro's new plan, although some were still upset about the condition of the streets.

"It's been mystifying to me how {Metro} can't order the use of water to keep down the dust," said Norman Wood, an Advisory Neighborhood Commission leader.

Others objected to the closing of U Street, but were told by Perini officials that keeping the street open would extend the time and cost of the project.

The first segment of the Green Line will serve some of the region's poorest residents. The second segment will connect the L'Enfant Plaza station and Anacostia, and the third segment will run between the Fort Totten station and Greenbelt. Those won't open until 1991 and 1993, respectively.

After months of dispute, Metro in May fired the original contractor, Mergentime/Perini Joint Venture, saying the firm was in default on its contracts to build the two stations. Perini had sold its interest in the joint venture in 1987 and was selected to complete the work.