The mayors also urged Congress to adopt comprehensive immigration reform, expand background checks for firearm purchases, and establish an "Office of Urban Agriculture."
Attendees also drew attention to the loss of jobs they said would occur in their cities if Congress goes ahead with a proposal to limit the tax-exempt status of municipal bonds.
During the four-day conference, big-city leaders including Los Angeles Mayor Antonio Villaraigosa also talked about struggles with crime and foreclosures while sharing leadership strategies.
Vice President Joe Biden gave the keynote address focusing on the need for gun control legislation. The Democrat-controlled Senate voted against legislation in April that would have expanded background checks for firearm purchases to gun shows and online sales.
The annual summer meeting of mayors was the first since the failure of the federal gun control push, and since Congress took up comprehensive immigration reform
Rampaging gunmen at Sandy Hook Elementary School in Newtown, Conn., and in a Colorado movie theater last year led to a renewed push for more firearm restrictions.
The background check resolution approved by mayors on Monday was sponsored by Chicago Mayor Rahm Emanuel and New York Mayor Michael Bloomberg, but neither attended the conference.
Newton Mayor Setti Warren said the congressional delay in implementing the checks was putting lives in danger.
"Because of a loophole in our system, criminals can avoid background checks by going to so-called private sellers to get guns -- and our communities are less safe because of it," he said in a statement.
Mayors from Philadelphia, Baltimore, Atlanta, Phoenix and about 200 other cities joined the voting on Monday. The organization represents 1,300 mayors from all corners of the country.
The marijuana resolution was sponsored by Revere, Mass., Mayor Daniel Rizzo.
The resolution declared that "states and localities should be able to set whatever marijuana policies work best to improve the public safety and health of their communities."
About 20 states now have medical marijuana laws allowing people to use pot for chronic pain and other ailments. Washington and Colorado recently legalized marijuana possession by people over 21.
Federal law, however, still criminalizes marijuana distribution and possession, and the Justice Department has repeatedly said it can continue to prosecute large-scale, privately owned marijuana operations that comply with state laws.
"Voters in states and cities that wish to break the stranglehold of organized crime over the distribution and sale of marijuana in their communities by legalizing, regulating and taxing marijuana should have the option of doing so," Mayor Stephen Cassidy of San Leandro, Calif., said in a statement after the passage of the resolution.
United States Conference of Mayors: http://usmayors.org
Hannah Dreier can be reached at http://twitter.com/hannahdreier .
Copyright 2013 The Associated Press.