Last Tuesday night, Democratic mayoral nominee John Street took the stage for Daily News columnist Stu Bykofsky's annual comedy night, told a few jokes and did something he hasn't done much since winning the primary in May.

Made himself visible to the public.

The Bykofsky charity event was one of only a couple of public outings on Street's schedule for the entire week, and aides say the former City Council president is even planning to take an official week of vacation time - albeit without leaving his North Philadelphia home - later this month.

In addition to keeping a light schedule throughout the summer, Street has taken some flak for missing Philadelphia events like the National Bar Association meeting and the Greek Picnic as well as failing to respond to Detroit Mayor Dennis Archer's offers to host a fund-raiser.

What's more, Street's longtime friend John F. White Jr., who ran third in the May primary but was popular with white liberals, the key swing voting bloc in the fall election, hasn't endorsed him yet and Street aides are starting to talk as if White never will.

Traditionally, voters have little or no interest in politics during the summer months. Some pundits say that Street wouldn't gain many votes - and indeed could lose a few - if he were running a frantic campaign in the heat of August.

"You do that on schedule," said Street's longtime adviser, Bruce Crawley. "You do that on the retail level when voters are ready for that."

He said that Street has been busy hiring staffers for the fall campaign, digesting polling data, raising hundreds of thousands of dollars and meeting with community-newspaper editors.

"If you look at the touching and the reaching out that he's doing, he's just not doing that in Center City," Crawley said.

Nevertheless, some political experts are starting to fret that Street is failing to cash in on an opportunity to woo white liberal swing voters during the slow summer months, while questioning his failure so far to win the backing of White.

"I don't sense that he is overly directed," said Obra Kernodle, a lobbyist and a key supporter of White in the May primary who is also close to Street. "But if you look at the primary, he was very structured and very studied in what he did."

Street has always been the kind of politician more at ease studying the latest budget proposal than kissing babies at a street fair, although he showed some signs of loosening up in the primary campaign when he posed for Polaroids with hundreds of voters.

Some political insiders familiar with Street's campaign strategy said the decision to run a low-key campaign has been a conscious one, because Street aides fear overexposure could hurt his poll numbers and or could somehow spark controversy in a race that he presumably leads.

Sam Katz, the Republican nominee, has been keeping a busy schedule this summer, attending civic group meetings and community picnics. The GOP financial consultant, who expects to match Street in raising about $5 million for the fall campaign, also dipped into the kitty to air some early TV ads to keep his name before voters.

Sunday through Friday last week, Katz held about 10 public events, including not only the Bykofsky fund-raiser but also a German-American celebration in Penn's landing, the opening of a day-care center at an Indian-American church, a coffee klatch with South Philly businessman and a speech at a Center City apartment complex.

Street's only other public event in that same six-day period was a picnic for African-American Democratic ward leaders.

"The summer is a time for retail politics, when you get out and meet voters one-on-one and lock them up for the fall," said Larry Ceisler, the Democratic political consultant and Fox-TV analyst. "Everyone you meet is gravy - in a close election, that guy that you meet at a street fair can mean something."

Ceisler, a political aide to former Mayor W. Wilson Goode, recalled that in the summers after his primary victories Goode would attend three or four coffee klatches with small groups of voters.

He said he wondered why Street is not doing the same thing, especially in areas like Mount Airy or Center City, where white liberals may be sitting on the fence between Street and Katz.

As pols look toward Labor Day and the traditional start of the campaign season, most agree that it will be very hard for Katz to overcome the 31/2-1 edge in voter registration that is held by Street's Democratic Party, which hasn't lost a mayoral election since 1949.

Indeed, sources who've seen the latest poll done for Street say the ex-Council president leads Katz by more than 20 percentage points. But political experts believe the race will tighten considerably as November approaches.

In addition to his GOP base, Katz is likely to carry many of the conservative rowhouse Democrats who backed Street's strongest primary foe, attorney Marty Weinberg. More importantly, pundits say, he will appeal to some of those liberal white voters who elected Goode in 1987 when he faced a strong November challenge from Weinberg's mentor, Frank Rizzo.

That's why an endorsement from White, the former housing chief who ran strongest in areas like Chestnut Hill, Mt. Airy, and Center City, of his longtime friend Street is considered vital. Such a nod was once considered a foregone conclusion and is still likely, though White is still slated to meet again this month with both Katz and Street before making a decision.

Street confidant Crawley shrugged off the whole issue of whether White will endorse his fellow Democrat, saying on Friday, "Maybe he will, maybe he won't." Crawley said the important thing is that campaign polling shows White voters, largely middle-class blacks and white liberals, are lining up solidly for Street.

While Happy Fernandez, the former city councilwoman, received just 6 percent of the Democratic primary vote, most of her support came from progressives who may also be torn between Street and Katz. Fernandez has also been coy about whether she'll endorse Street.