* Q1 underlying op. profit 302 mln euros vs forecast 306 mln * Earnings weighed down by weakness in oil refining * Comparable sales margin rises at renewables business (Releads, adds shares, analyst) HELSINKI, April 29 (Reuters) - A strong performance at its main renewables business lifted shares in Finland’s Neste on Thursday, after weakness in refining drove an expected fall in first-quarter earnings. Underlying operating profit for January-March fell to 302 million euros ($366 million) from 408 million euros a year earlier. That compared with the 306 million euros expected by analysts, according to Refinitiv Eikon data. “Operationally, Neste delivered good performance in its core Renewables business despite rising feedstock prices while Oil Products remained impacted by weak refining margins,” Citi analysts said in a note. Neste shares were up 3.6% to 52.98 euros at around 0800 GMT. Neste’s renewables unit, its main profit generator, reported a fall in operating earnings to 294 million euros from 329 million a year earlier, mostly due to changes in foreign exchange rates. The comparable sales margin at the unit rose to $699 per tonne from $685 despite higher feedstock costs. The firm highlighted robust demand for waste and residues it uses as inputs. “The rise in raw material prices has caused worries, and the gross margin there was at a very strong level, allaying some concerns,” said Inderes analyst Petri Gostowski.