Of the 307 bridges in Pittsburgh, 20 percent are "structurally deficient," but none is unsafe, said a group of city, Allegheny County, state and federal officials at a City Council session yesterday.

Engineers rule a bridge deficient when any part of it, such as its deck or superstructure, shows any marks of deterioration.

Many of the city's bridges are getting older and will need to be rehabilitated in coming decades, leading council and the Ravenstahl administration to consider plans for long-term maintenance and budget issues.

The Pennsylvania Department of Transportation maintains 205 of the bridges, but the city plans to renovate three of its problem spans next year: McArdle Roadway viaduct No. 1; the East Liberty pedestrian bridge; and the Eliza Furnace Trail bridge at Bates Street. In coming years, it plans to rehabilitate spans on West Carson Street, South Highland Avenue and Davis Avenue.

When inspectors find a bridge unsafe, it is closed immediately, as the Birmingham Bridge was in February, said PennDOT District 11 engineer Dan Cessna.

In a related matter, Mr. Cessna updated council on the rebuilding of Route 28 south of the 31st Street Bridge. PennDOT has purchased 15 houses along the four-lane road that will soon be razed, and plans are under way for shifting rail lines that lie between the road and the Allegheny River.

It is also planning upgrades to Butler Street and other city roadways, as they will face overflow traffic during Route 28 reconstruction. One of the northbound Route 28 lanes will be closed for several years during construction, Mr. Cessna said.