UPDATE 1-RPC sees H1 adj pretax profit up vs last year

* Says H1 revenue will be lower than last yr as expected * Says volume shortfall offset by margin restoration

* Sees lower interest charges in H1 * Shares rise 5 pct to new 52-week high (Adds details) Sept 23 (Reuters) - RPC Group Plc (RPC.L), a supplier of plastic packaging, said on Wednesday it expected its first-half adjusted pretax profit to be ahead of last year as a fall in sales volume was more than offset by a restoration of margins and lower costs.

The company said its revenue for the six months ending September would be lower than the same period last year, as previously expected, as polymer price-cuts were passed through to customers, reducing overall volumes.

RPC said it expected interest charges to be significantly lower due to lower rates and reduced average net debt.

"I believe that RPC's prospects are good with overall industry dynamics improving and our self-help plan RPC 2010 delivering as promised," Chief Executive Ron Marsh said in a statement.

RPC shares rose 5 percent to their 52-week high of 261 pence by 0728 GMT on the London Stock Exchange. (Reporting by Tresa Sherin Morera in Bangalore; Editing by Gopakumar Warrier)