I want to say 'it was said'. I have noticed that the autonomous verb 'Duradh' fits the bill. However, I have also noticed 'Bhi se raite' used also. My question is can I us these two phrases to same the one thing?

It depends. They're are not completely equivalent. If somebody specific said something, use dúradh. If it was "the talk of the town" use bhí sé ráite.

Even those of us who use Irish every day can fall into a number of pitfalls when we use the aidiacht briathartha and the briathar saor (autonomous).

Sometimes one sees in reference to a book "Bhí sé foilsithe 2009." If that means "It had already been published by the year 2009" that is OK but if it first appeared in the shops in 2009 the briathar saor should have been used. So the book was published in 2009 would be "Foilsíodh an leabhar 2009." (Why no prepositions etc to garnish the 2009? I think 2009 is treated as an adverb and the meaning is clear.)

So to answer your question if the meaning is "It was said (by someone whom we need not refer to now)" use "Dúradh".

Avoid "bhí sé ráite" unless the emphasis is on what had been said. Bhí sé ráite aige sular chuimhnigh sé air féin. He had it said before he thought of himself.

The autonomous verb is a very distinctive feature of Irish and should be used. The English construction "It was said" is a trap for the unwary, a pitfall for the learner unfamiliar with written and spoken Irish and relying solely on the dictionary and the grammar book. Sadly as bilingualism progresses and English becomes dominant in the Gaeltacht such distinctive features are likely to be lost. Bí san airdeall. Seachain an botún seo.

I also think the verbal adjective is meant to be used only for completed states. I think in the context of beginning a sentence, "dúradh go..." would work for the proverbial use of "it was said that ...". At the end, "bhí sé ráite" would be better as an ending thought, placed after a comma, kind of like what Aonghus says about "the talk of the town".

In Donegal : húradh go...

Go raibh maith agaibh.