The managing director of Italia di Navigazione SpA is expected to submit his resignation May 18 at the company's annual meeting in Genoa, according to reports coming from Italy.

Mario Ferrando, general manager of the state-owned shipping company known as Italian Line, confirmed Monday that Roberto Colonnello would leave the company at the end of May. No replacement has yet been named, he said in a telephone interview from Genoa.Mr. Ferrando said any further comment would have to come from Mr. Colonnello himself, but he was unavailable for comment Monday.

Maurizio Massa, owner's representative for Italian Line in New York, said there was no official confirmation of the news but that press reports from Genoa indicated Mr. Colonnello would assume the presidency of Compagnia di Navigazione Merzario SpA, Milan.

That company operates liner services connecting North Europe to the Mediterranean, the Middle East and the Indian subcontinent. It owns and operates two 21,000-deadweight-ton roll-on roll-off vessels that it uses in a liner service connecting ports on the Adriatic Sea to those in the Middle East.

It also owns a container fleet of more than 30,000 cargo containers and operates several liner agencies.

In December 1989, Merzario was purchased by CMB Transport, a unit of CMB SA, Antwerp, Belgium. CMB, in turn, is part of the holding company Societe Generale Belgique SA, also of Antwerp.

Mr. Colonnello leaves Italian Line as the company's modernization program nears completion. During his tenure, new, larger containerships were added to the company's service between the Mediterranean and the United States. More such ships are on order for a separate service between the Mediterranean and South America.

In addition, the line's agency structure in the United States was completely revamped with the establishment of its own agency company devoted solely to Italian Line business.

Mr. Colonnello, however, was never able to make the company profitable in his five-year tenure. Observers say Italian Line has been a consistent money loser since it converted from a breakbulk operator to a container shipping company in the 1970s.

The company is expected to post a 6.8 billion lire (US$5.5 million) loss for 1989 when the annual meeting is convened May 18. That loss is an improvement over the 26.7 billion lire loss for 1988.

Italian Line carried 797,680 tons of cargo on 316 voyages on all its routes last year, according to figures released by the company.

Its U.S. service last year ranked 40th in volume among all liner carriers serving the United States, according to information compiled by Port Import/ Export Reporting Service, or PIERS, a division of The Journal of Commerce.