The union for the city's blue-collar workers amped up its contract tough-talk this week, running a series of radio ads slamming the city.

The five ads are appearing on several local stations, including WURD (900-AM). They feature workers in District Council 33 of the American Federation of State, County and Municipal Employees describing their duties. At the conclusion of each spot, DC 33 President Pete Matthews says:

"DC 33 members work hard every day to provide all the city's most vital services. Now Mayor Nutter wants to punish them by cutting their jobs, health and pension benefits. It is time for the mayor to settle a fair contract that gives our members the respect they have earned."

Mayoral spokesman Doug Oliver responded yesterday, saying the city was committed to a fair contract, but "it must also be fair for the 1.4 million Philadelphians who will pay for it."

Oliver added: "The only way we will be able to negotiate anything is if we are joined at the negotiating table by Mr. Matthews."

Contracts for the city's four municipal unions expire on June 30. But so far negotiations have been moving slowly. The city has not sat down with DC 33 or the city's white-collar union, District Council 47, in more than a month.

"If we're talking concessions, meeting is pointless," Matthews said. He declined to say how much the union was spending on the ads.

With the city battling a fiscal crisis, Nutter has said employee costs must be reined in. As part of his budget, which is dealing with a $1.4 billion five-year shortfall, Nutter eliminated money set aside for raises and is counting on getting $125 million in contract savings over the next five years.

The city's opening offers to the nonuniformed workers included a four-year wage freeze and major concessions in pension contributions and work rules, as well as a major restructuring of health-benefit plans.

Contracts for the city's 10,000 uniformed workers - who cannot strike - are settled through arbitration. That process started for police last month and is scheduled for firefighters later this year.

Unlike police and firefighters, the 10,000 members of the nonuniformed unions can hit the pavement. And sources tell the Daily News that the city has begun making preparations in case of a strike.

The last major municipal strike was a 20-day walkout in 1986, when piles of garbage rotted in the July heat. Eventually, then-mayor Wilson Goode declared a health emergency and forced employees back to work.

Today Nutter was scheduled to attend a U.S. Conference of Mayors meeting in Providence, R.I., where firefighters are on strike. Vice President Joe Biden has canceled his appearance at the meeting because the firefighters plan to picket. *