Democratic presidential hopeful Barack Obama has received an honorary doctorate after addressing college graduates in Connecticut.

In his speech at Weslyan University, the Illinois senator urged the audience to dedicate themselves to public service.

He devoted special attention and praise to Edward M. Kennedy, the long time Massachusetts senator who had planned to deliver the graduation address but backed out last week after he was diagnosed with a cancerous brain tumour.

Kennedy has endorsed Obama in the nominating contest against fellow Democrat Hillary Clinton.

Meanwhile, Obama sought to quell the dispute surrounding Clinton's comments about the long primary process, in which she mentioned the 1968 assassination of Senator Robert F. Kennedy.

Some accused Clinton of making a veiled reference to another major assassination of 1968 - of the Reverend Martin Luther King - and to the possibility that Obama might be killed, leaving her a clear path to the nomination.

Clinton said the remark had been torn out of context and twisted into something "completely different - and completely unthinkable."

Obama told reporters that the episode should be forgotten.

Clinton is spending the Memorial Day weekend campaigning in Puerto Rico which offers 55 pledged delegates to the national Democratic convention.

The New York senator is expected to win Puerto Rico's primary on June 1, thanks partly to her ties to the large Puerto Rican community in her home state.

Clinton said she will stay in the race despite trailing Obama by nearly 200 delegates, with 2,026 needed to win the party's nomination.

Obama was about 50 delegates short of the number needed to win - and Clinton says she will keep going until one of them does.

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