New Democrats have agreed to defer a vote on whether to drop the word "socialist" from its constitution, and rejected a resolution that would have banned a merger with the Liberals.

At the NDP's 50th anniversary convention in Vancouver, the party was confronted with how to present itself as the new Official Opposition in Parliament, and how to close its 50-seat gap with the Conservatives.

The debate over the world "socialist" put the party in a tight spot between its core, pro-union supporters and the more centrist voters who fuelled its success in last month's election.

"On one hand they want to retain their ties to labour, but on the other they're looking for ways to expand the base, expand the appeal to include others who don't support labour at all," said CTV's Richard Madan.

Proponents said the constitution, which was written half a century ago, needs to be "modernized." Others said dropping the reference to socialism would separate the party from its roots.

The preamble to the current constitution says social, economic and political progress is possible "only by the application of socialist principles" such as state control over the production and distribution of goods and services.

Meanwhile, on the question of whether the NDP would ban a merger with the struggling Liberal party, members like Nova Scotia MP Peter Stoffer said it would be a "serious tactical mistake."

He said if the NDP ever hopes to form a government, it will need Liberals to switch sides.

"We don't get Liberals if we say, 'Because you're a Liberal, we no longer have talks with you,"' he told The Canadian Press.