On the eve of the Democratic Convention, the solidarity of public employees and the commitment of delegates not to cross their picket lines secure contracts: The firefighters were the last big city union left without a contract. In the days leading up to the convention on Monday, there had been concerns that union strife might interfere with the four-day event....The convention begins Monday, but delegates began descending on Boston over the weekend. Scores of welcoming parties were planned throughout the city Sunday. Unionized city police officers reached a four-year deal with the city several days ago, but had said they would still picket Sunday night delegation parties to show support for firefighters. Firefighter union leaders said they no longer intend to picket. And unionized police officers said they were backing off the threat as well...The agreement with police officers was reached last week after it was sent to expedited arbitration. The police had sought 17 percent pay increase over four years, while the city's last would have provided 11. 9 percent. The independent arbitrator picked a figure roughly in the middle, 14.5 percent. The firefighters' union, like its brethren nationally, has strong ties to Democratic presidential candidate John Kerry. Boston's municipal labor unrest has presented a problem for the party, its labor-friendly delegates and Kerry for months. Faced with protesting officers at a recent mayor's conference, Kerry declined to cross their picket line to deliver a speech. ``Everybody looked around the room and smiled and felt like, finally, we can concentrate fully on the convention,'' Josh White, executive director of the Maryland Democratic Party, said Sunday. The 99-member Maryland delegation had said it would not attend any function that required crossing a picket line. Other state delegations had issued similar threats. The Democratic Convention schedule is on-line here.