Top administrators of the longshoremen's union and steamship companies told Maryland legislators yesterday they have pledged to collaborate to improve the competitiveness of the Port of Baltimore and erase its image as a port torn by labor strife.

"We are forming a new team for the port, a tool for progress," said William J. Detweiler, president of the Steamship Trade Association of Baltimore, in announcing the new agreement with the International Longshoremen's Association and the Maryland Port Authority.

He made the announcement before a House subcommittee as the General Assembly considered creating a new commission to oversee the port, giving it relative freedom from state regulations over personnel and purchasing. Gov. William Donald Schaefer contends such autonomy would improve the competitiveness of the port, which has been losing business to East Coast rivals, including the ports in New York and Norfolk.

The longshoremen's association and the steamship companies forged a similar agreement last year, but it quickly broke down. Detweiler and longshoremen's association officials predicted yesterday the new effort would prove more durable, because it was initiated by them, rather than by the port authority, which had brokered last year's widely publicized agreement.

After the announcement, Del. Timothy F. Maloney (D-Prince George's), chairman of the House subcommittee on law enforcement and transportation, said the new truce would improve the port administration's chances of getting budget increases it is seeking. "It isn't going to hurt," Maloney said, "because if they start fighting and it hurts the perception of the port, they're not going to get the money."