A mayor's race that has seemed so lackluster burst into the public arena yesterday. The two major candidates changed advertising strategies from soft ads about nice guys with good ideas to direct appeals to swing voters that crossed racial and party lines.

And they trotted around the city working the electorate.

On television, Republican Sam Katz's ads touted his endorsement from a popular African American Democrat, John White Jr., who came in third in the spring primary behind John F. Street. The Street campaign plans to begin airing an ad today showing a popular white Democrat - Mayor Rendell, who was just anointed chairman of the Democratic National Committee.

Given the 4-1 Democratic registration edge over Republicans in the city, both men are fighting over swing Democrats.

In receiving a mid-morning endorsement from Democratic District Attorney Lynne M. Abraham yesterday, Street won the support of someone who appeals to liberal and conservative white Democrats. Rendell, one of Street's most prominent supporters, appeared in ads for him during the primary.

For Katz, White's endorsement is a powerful message to liberal whites and middle-class blacks that it is OK to vote for a white Republican.

The Katz ad says, "Now, thousands of Democrats throughout the city are supporting Sam Katz for mayor. Led by former mayoral candidate John White Jr., Democrats and Republicans are coming together."

Street's Rendell ad delivers a similar message by calling the African American Street a "coalition-builder."

Katz and Street supporters have been trying for weeks to nail down an endorsement from Henry Nicholas, head of the National Union of Hospital and Health Care Employees, District 1199c. Nicholas said yesterday that he had received overtures from both campaigns and even met with Jerry McEntee, his union's international president, in Washington on Wednesday about a Street endorsement. He said he wanted to keep on dancing so he would be "the most wanted man" in Philadelphia: wanted by Katz and wanted by Street.

"It's too early" to endorse, Nicholas said. "I'll be on the most-wanted list in two weeks from both camps."

Both major-party mayoral candidates kept up rigorous paces yesterday. Street spoke to the Delaware Valley Grantmakers, union carpenters, shopping center executives and Center City residents, shook hands at Fourth and South Streets, and surveyed, with Abraham, a troubled North Philadelphia neighborhood where community leaders are fighting blight.

Katz was no slouch either. He preached economic salvation to 250 businessmen and women at the Union League, testified in favor of campaign finance reform at legislative hearings at the Convention Center, spoke to the shopping center executives, and met with Center City residents.

In accepting the Abraham endorsement during a press conference at the corner of 10th Street and Indiana Avenue, Street promised "additional resources" for her fight against drug crimes. That is government-speak for more money.

Street and Abraham had been at odds for years while Abraham fought for more money to support her anti-drug efforts. Street said that he was unable to increase funding to the district attorney while he was Council president because the city's first task was to balance the budget.

Now that the city has more money, he said, he would be able to help Abraham.

The press conference location was chosen because it is near Fairhill Cemetery, which was a trash-strewn drug market and homeless hotel until two years ago when neighborhood leaders cleaned it up, according to neighborhood activist Peaches Ramos.

As mayor, Street said, he would support such efforts.

Downtown at the aristocratic Union League, Katz said that Philadelphia must capitalize on its location near major highways, rail lines and shipping channels, on the inclination for some developers to build shopping centers in urban areas, and on the city's work force, which he said is large but needs better training and education.

Katz hinted that he may soon disclose his plans for cutting wage and business taxes more deeply than Rendell did. He said tax cuts over the last five years and those planned for the next five years would have "no impact" on disposable income or corporate decisions to locate in Philadelphia.

He also took a shot at Street for not appearing at the Union League yesterday, saying that because he was "absent without leave," attendees were denied a chance to draw comparisons between the two candidates.

The League's tradition is to have both general election candidates attend a public-affairs luncheon. Its president, Jim Straw, said that in the summer the League asked both candidates to suggest several dates but that Street did not lock in a date until last week.

He will speak to the group Oct. 19, Straw said.

Defending Street's absence, his spokesman Ken Snyder said, "Until we find a way to clone John Street, he's not going to be in two places at one time."

During the league luncheon, Street was addressing shopping center executives at the Convention Center.