Teams of local, state and federal officials are doing preliminary assessments of tornado damage in seven Minnesota counties today.  Information they collect will help determine whether Governor Pawlenty requests a major disaster declaration from President Obama.  Meanwhile, with most of the counting done, weather officials say there were 18 tornadoes which swept through Minnesota last Thursday.  Preliminary numbers also account for three E-F-4 twisters -- in Wadena, Almora and near Albert Lea.   There were several E-F-3 tornadoes, mostly in Freeborn and Steele counties.  Three people died in the storms late last week and dozens across the state were injured.