The Alexandria Democratic Committee has become the fourth Washington area Democratic group to call for an open convention at next week's national party gathering in New York.

The Alexandria Democrats voted 43-18 Monday night in favor of a resolution that urged the release of delegates from pledges to support President Carter or any other presidential candidate. Though the president has already won more than enough delegates to be renominated, some Democrats say his low standing in the pools justifies allowing delegates to consider other choices.

"The leadership of the committee was all pro-Carter in the spring when the convention delegates were elected, but now some have taken a drastic change," said Cecily Coleman, an Alexandria delegate who supports Sen. Edward M. Kennedy.

Coleman said the lopsided vote for an open convention was particularly noteworthy because Carter received more than 60 percent of the city's support at mass meetings held last March to select convention delegates.

Nancy Arnsen, a leader among Carter delegates, opposed the open convention resolution at the Monday night meeting. She could not be reached for comment yesterday.

Though Carter supporters say the open convention movement will have little impact on Virginia's delegation and its 59 Carter backers, other Virginia Democrats said yesterday that Kennedy or another candidate could still benefit from the erosion of Carter's following.

Democratic committees in Fairfax County, Prince William County and Maryland's Montgomery County previously endorsed resolutions of support for an open convention.