Engineers planning the replacement of the I 35W bridge over the Mississippi in Minneapolis were told today to be aware of issues which may slow their ambitious rebuilding schedule. Minnesota officials are promising the ribbon will be cut on a new span a year from this fall. However various local officials want planners to allow time for more public comment on the design of the new bridge. And University of Minnesota vice president for operations Kathleen O'Brien reminded state officials that removing the debris of the old span and construction of a new one will occur literally a few yards from one of the U's research facilities. State officials put the price tag of a new 35W bridge at $250 million. However, they say the cost could rise to well over $300 million when demolition and other expenses are added.