St Lawrence Cement Group, Canada, reported lower fourth-quarter profits and sales Wednesday.  The Montreal-based cement and construction products producer said it earned $21.8m or 53 cents a share for the the three months ended Dec. 31. That compared with profits of $24.9 million or 61 cents a share for the same 2002 quarter.  Sales fell to $321.1 million from $327.2 million.  Sales volumes improved for cement, aggregates and concrete, reflecting good demand in all markets. However, that was offset by lower cement selling prices the US market, compounded by the weaker US dollar as well as lower sales of construction services.