Mayor W. Wilson Goode announced tonight that 2,400 city trash collectors are expected to return to work by 7 a.m. Saturday and end an 18-day strike during which tens of thousands of tons of trash have been dumped in huge piles around the city.

Goode said the trash collectors will work "all weekend and on Monday" to clear the 15 city-designated emergency dump sites.

James Sutton, president of Sanitation Workers' Local 427, and John Dykes, its business agent, assured the mayor that the workers will be at work Saturday morning, Goode said.

He added, however, that any trash collectors who do not arrive at work by 7 a.m. will be fired.

Goode, who has threatened for several days to fire the striking trash collectors, said tonight that "we have 20,000 potential workers on the list who are prepared to start."

If the striking sanitation workers do not appear as promised, he said, the city will call in private contractors to clear the dump sites.

At least 20 workers reported back to work today, the mayor said.

Union officials were not available for comment.

District councils 33 and 47 of the American Federation of State, County and Municipal Employees called a strike of 13,000 city workers on July 1. Thousands of the original strikers remained out of work today, many of them in sympathy with the sanitation workers, whose local is part of District 33.

Today's agreement came after efforts by Goode to force the trash haulers back to work.

On Wednesday, Common Pleas Court Judge Edward J. Blake issued a back-to-work order for the trash collectors after hearing testimony by city officials that the emergency dump sites were threatening the public's health and safety.

Almost all of the trash haulers, who are members of Local 427, ignored the order, and this morning Blake found them and District Council 33 in contempt of court, and told the city it had the right to fire the strikers. Blake also levied a $40,000-per-day fine against District Council 33, to begin Monday, if the strikers did not return to work.

Earl Stout, president of District Council 33, said today that his union will appeal the contempt citation. He did not comment on the decision by Local 427's leaders to order their striking workers back on the job.

There has been no progress in contract talks between the city and the striking sanitation workers, and negotiations have been on hold since Wednesday.

Asked tonight whether the two sides are any closer to signing a contract than when the strike started July 1, Goode said, "For the most part, we're not."

The major sticking points include the size of a pay increase, the length of the new contract and whether the city will be allowed to audit the union's books, authority it does not have.

Philadelphia is the only major city in the country that does not have the authority to audit one of its unions, according to the Pennsylvania Ecnomoy League, an independent study group. The unions of other Philadelphia city workers do allow audits.

The mayor said tonight that he is moving to resume negotiations immediately, but that he will insist that the city be allowed to contract out sanitation work and that it be allowed to audit the district council's books.

The city will clear the emergency dumps first, then remove trash that has been left on streets and in parks. After that, it will resume regular garbage collection. Goode said tonight he had no idea when that would happen.

The mayor told residents to keep trash at home rather than dumping it.

Asked whether he was attempting "union-busting" by threatening to fire the trash collectors, Goode said he was not, and that he had put the health and welfare of the public first.

Stout, head of District Council 33, supported Goode's mayoral campaign in 1983, and labor votes were important in his election.

Asked whether his tough stand now might hurt his chances for reelection next year, Goode said he didn't care.

"I'd rather be right on the issues than be mayor," he said. "If it costs me the election, I'll live happily ever after."

Goode said the strike had gone on this long because he had waited to seek a back-to-work order until the city had sufficient grounds for it, namely the the dumps posed a danger to public health and safety.

Picketing sanitation workers angrily rejected that argument on Thursday. As one worker put it, "We work in the stuff every day."