The Soviet Union has published its emigration rules for the first time, saying they have been revised to speed up applications. But the new code also gives authorities broad grounds for denying exit visas. In the past, applicants said exit visas were granted or denied without explanation. Foreign Minister Eduard A. Shevardnadze said last week that new laws were being adopted to develop international contacts and "resolve in a humanitarian spirit" problems of family reunification. But the new regulations, which take effect Jan. 1, appear to codify existing procedures rather than significantly loosen emigration policy.