President Reagan all but assured urban leaders today that he would support an extension of the popular revenue-sharing program, which returns federal funds to states and municipalities.

The president said that he had supported revenue sharing over the last two years, "and while I haven't made any final budget decisions for fiscal 1984, I can promise you I will look at revenue sharing in the same light." The $4.6 billion program is up for reauthorization next year.

But, at the same time, Reagan cautioned that the cities had become "addicted to federal bailouts" and would have to become more self-reliant.

He told more than 3,000 delegates to the National League of Cities convention here that new federal spending programs are not the answer to their economic problems. "It is time to give up the temporary Band-Aids and placebos," he said. " . . . In a very real sense, our coffers are empty."

The president also asked the league to support his proposals for a gas-tax increase to repair aging roads and bridges and for creation of enterprise zones in 75 distressed neighborhoods.

League officials generally were pleased with Reagan's conciliatory tone, especially on revenue sharing. "I feel very encouraged by some of the things he said," league president Ferd Harrison of Scotland Neck, N.C., said.

But George Latimer, mayor of St. Paul, Minn., said Reagan's speech broke no new ground. "With the hardships we're facing in the cities, we're a little less enthusiastic about self-reliance making the difference," Latimer said.

Reagan singled out Baltimore's "Blue Chip-In" program as an innovative approach in which private companies have donated money or jobs to hire the unemployed. But Baltimore officials say the contributions made up only 1,751 of the 12,000 summer jobs they lost to federal budget cuts. As for permanent jobs, the companies have raised only $2.2 million of the $63 million the city has lost in federal job funds.

"I think it's clear the private sector cannot be expected to pick up the entire gap in these hard economic times," said Steven Kaiser of Baltimore's manpower office.

In similar fashion, many of the officials here have been on a starvation diet for two years and are resigned to a prolonged period of austerity. Dayton, Ohio, is buying its own phone system, Fort Worth has hired a company to pick up the trash, Minneapolis has gone to one-man police cars, and while firemen in Seattle still put out fires for free, they now charge to conduct building inspections.

One of the busiest exhibitions at the convention belongs to Wackenhut Services Inc., which contracts with cities to provide firemen, ambulances, airport rescue teams and, for small towns, entire police departments. Wackenhut official George Zoley said Hall County, Ga., has saved $200,000 annually in firefighting costs because Wackenhut does not have to pay union wage scales or municipal pensions -- an approach he conceded is highly unpopular among public employe unions.

Dayton commissioner Abner Orick said that his city now charges fees for everything from playing golf to buying a handgun. There is even a $3 charge for a meterman to inspect a homeowner's sink.

Dayton used to have three-man teams who picked up trash at 330 homes a day, Orick said, but new equipment now enables a single driver to reach 600 homes a day. In addition, he said the city is paying a private firm to put up a new office building, which officials then will lease at a cheaper cost.

But other cities are less well equipped to weather the storm. In Minneapolis, Mayor Donald Fraser has had to lay off 10 percent of the city's work force and to cut police and fire protection to the lowest point in a decade. He has also slashed services from libraries to street cleaning.

Fraser said corporations in his city already are pledging 5 percent of their pre-tax earnings for social needs, but "they say themselves that the withdrawal of federal aid is far beyond their ability to pick up."

In Seattle, Mayor Charles Royer has had to eliminate his energy department and consumer protection office. "You can only raise parking meter fees so high," Royer said. "We've already pushed these to the limit."

Most of the convention workshops are designed to teach officials how to get by with less. "Last year, we were all just bemoaning the 'New Federalism,' " said New York City Council President Carol Bellamy. "Now we're talking about fees and contracting out and other substitutes rather than how to get the federal dollars back.

"When you're pushed against the wall, sometimes your legs get stronger."