A federal judge here blocked state plans yesterday for a multimillion dollar project to dump mud dredged from the bottom of the Baltimore Harbor on tiny Hart and Miller islands in the Chesapeake Bay.

Judge Herbert F. Murray said the U.S. Army Crops of Engineers "exceeded its authority" by failing to consult the U.S. Congress before it issued the permit in 1976 to buildtwo-mile-square dikes on the islands to hold the tons of mud in place.

Some of the attorneys and officials involved with the project said they think Murray's ruling will have a broad impact nationally and force the corps to seek congressional approval of many projects already in progress.

"I believe this opinion will have far-reaching effects," said Edward B. Rybczynski, attorney for the Hart and Miller Islands Area Environmental Group. "This decision will be very persuasive. I've already received calls from all over the country asking about the case."

A spokesman for the corps in Washington said its attorneys would not comment on the impact of the opinion or how many projects would now need congressional approval until they have thoroughly read the opinions, probably next week.

The corps had argued that congressional approval is needed only when the project crosses an entire navigable body of water.

Murray disagreed, saying that whenever a project is built in any navigable waters involving more than one state, Congress must decide whether that project is permissible.

The Hart and Miller Islands project has been fiercely protested by area environmental groups and Maryland's Rep. Clarence D. Long. They charged that the planned dikes would break or that hazardous metals and chemicals from the harbor mud would pollute the relatively clean waters of the bay.