Alongside the nation's plague of spy scandals, Washington had another abuse of sensitive Government information to ponder last week. Commerce Secretary Malcolm Baldrige announced the dismissal of three unnamed employees at the department's Bureau of Economic Analysis. Their offenses: two were found to have used advance knowledge of the Government's quarterly estimates of economic growth for personal gain, while the third passed along the information for an outsider's gain. It was the first time ever for such punitive action. Said Baldrige: ''We have a duty to maintain credibility and integrity.'' The firings came after an eight-month investigation following charges that the GNP estimates, which sharply affected the performance of U.S. financial markets on the day of their release, were leaked to Wall Street traders twice last year. The results of the inquest were severely disquieting. At least 60 bureau workers--well beyond the authorized limit--knew the secret numbers, and investigators could not tell who might have slipped information to outsiders. The three dismissed for breach of trust, on the other hand, were hardly big- time offenders: one of them made only about $300 in the bond market.