Pollution from coal-burning power plants is on the rise in the U.S., spurred by competition in the electric market that has encouraged utilities to rely more heavily on the cheaper power generation method of burning coal, two environmental groups charged in a report yesterday. Electricity production from coal-burning power plants rose 16 percent from 1992 to 1997, producing an additional 755,000 tons of smog-causing pollution each year, the Environmental Working Group and U.S. Public Interest Research Group reported. Spokespeople for utilities denied that competition has had a significant effect on pollution levels.