The Coast Guard officier whose actions were blamed for a collision that killed 11 servicemen was sentenced today to receive a letter of reprimand and a token reduction in seniority for his role in the accident.

The verdict, issued by a military court, will have little practical effect on Chief Warrant Officer Donald K. Robinson, 48, skipper of the cutter Cuyahoga.

Moments after he was sentenced, Robinson said he soon will retire from the service. Neither the formal letterof reprimand he will receive nor the loss of ranking among other warrant officers is sufficient to block him from receiving a full military pension, retirement benefits, and an honorable discharge.

"I'm very happy with it," said Robinson, a 27-year Coast Guard veteran who dashed into an anteroom with tears in his eyes to thank the jurors after the sentence was pronounced.

"It's been a very long year and we're glad it's over with."

The jury, which on Saturday had found Robinson guilty of dereliction of duty, could have sentenced him to as much as three months in jail at hard labor and dismissal from the service -- a punishment equivalent to dishonorable discharge that, would have meant the loss of his pension.

Instead, the jurors, who spent an addition two hours and forty minutes deliberating Robinson's sentence today apparently heeded the plea of defense attorney Jerome V. Flanagan. He told them this morning that Robinson had already suffered enough for his role in the mishap, the worst Coast Guard disaster in more than 10 years.

The sentence will be routinely reviewed by Coast Guard Commandant Adm. John B. Hayes and Transportation Secretary Neil Goldschmidt, who have the power to reduce it or throw out the verdict. Court officials said the review process could take up to a year, after which Flanagan said he plans to appeal the case to either a military or a federal court.

Today's sentencing ended the two week trial at the Coast Guard Reserve Training Center here, where the Cuyahoga was based before the tragedy

The 51-year-old cutter was on a training mission on a calm, clear night on Oct. 20, 1978 when it was rammed by a large Argentinean coal freighter in the Chesapeake Bay near the mouth of the Potomac River. The vessel sank less than three minutes later.

Coast Guard investigators held Robinson responsible because he turned the cutter into the path of the frieghter minutes before the collision. Robinson testified that he had mistaken the 521-foot-long, 30,000 freighter for a small fishing boat, and had neglected to watch it closely on radar or attempt to make radio contact its pilot.

Robinson was originally charged with involuntary manslaughter, destruction of government property and negligence -- charges that could have resulted in up to five years imprisonment. The first two charges were dropped last June when a military judge ruled that the Coast Guard would have to renew its investigation to justify the allegations.

Chief prosecutor Cdr. James F. Meade, said after the sentencing that the Coast Guard did not plan to revive the other charges in the case. "As far as we're concerned it's over," he said.

Meade would not comment on the verdict or the sentence. "It doesn't make any difference whether I'm satisfied or not and I'm not going to say," he said.

After 12 hours of deliberation ending Saturday, the jury rejected the negligence charge -- which carried a maximum penalty of two years in jail and dismissal from the service -- but found Robinson guilty of the lesser dereliction of duty charge.

Dressed in his officer's blue uniform with his wife Margaret sitting directly behind him, Robinson listened to the arguement over his punishment this morning with the same calm, impassive expression he had displayed throughout the court martial.

Defense Attorney Flanagan, pleading for either no punishment or reprimand, cited findings or a Coast Guard investigative board in arguing that fault for the accident rested more with the Coast Guard than with Robinson.

The board concluded last August that the Cuyahoga was not adequately manned, that the ship lacked proper emergency lighting, wheelhouse radar equipment and watertight doors. All of these deficiencies contributed to the tragedy, the board said.

Flanagan also cited testimony from medical experts and from Robinson's family that the officer suffered from sleeplessness due to a lung ailment that military doctors failed to diagnose.

Asked what he would say to the families of the 11 dead crewmen, Robinson paused in the courtroom and replied: "I don't think it would be an appropriate time to say anything.