After a three-week shutdown, the biggest show in town resumed production yesterday as striking actors and struck producers returned to the bargaining table in the company of a federal mediator.

With the 32-day-old strike affecting virtually every level of the motion picture and TV industries, the hope is that a settlement will be reached by Labor Day.But hopes are not high.

Some 5,000 striking actors didn't appear worried yesterday as they massed in front of the Disney Studios in Burbank. As in previous demonstrations at the Burbank studios (Columbia Pictures and Warner Bros.), 20th Century-Fox and Universal, the picket line was largely symbolic, with a 10 a.m.-'til-noon time limit aimed at grabbing media attention.

The two sides had broken off talks over the issue of cable TV, videocassette and videodisc residuals, with members of the Screen Actors Guild and the American Federation of TV and Radio Artists demanding profit participation from the first dollar when projects in which they appear are sold to those markets. The Association of Motion Picture and TV Producers countered with an offer of profit participation after a two-year period of exhibition.

'No studio is going to give the actors what they're asking for," a Universal Studios executive said yesterday. "If the actors give in on their demands, the strike will end. If not, it could go on until March and we're okay. We have products to release through June of 1981. United Artists has 24 pictures on the shelf, enough for 18 months. MGM has six or seven.Paramount is good until the fall of 1981. So the producers are not worried."

This week, the actors showed equal determination. On Wednesday, SAG anounced a Sept. 16 benefit to raise money for its emergency fund; and 46 actors including Ed Asner, Alan Alda, James Garner and Larry Hagman) pledged to boycott the Sept. 7 Emmy Awards as an "individual choice of conscience." And on Monday, the union changed its policy on interim contracts with producers during the strike.

Since the strike began on July 21, SAG has been allowing independent producers to continue filming on location if they signed "interim agreements." More than 60 producers of feature films and TV productions signed the agreements, which required that the producers agree to compensate actors according to the SAG demands that were on the table at the time the talks broke off. The terms of each interim agreement differed, but all included percentages of gross revenues from the new video markets. In the event the strike is settled on terms other than those currently on the table, the producers will not be held to the interim agreements.

On Monday, however, SAG ended its policy of interim agreements in favor of offering production companies permanent three-year contracts that will not be adjusted to reflect the terms eventually agreed to by the producers' negotiating committee.

The new contracts contain tougher terms and include 35 percent across-the-board pay raises, and increased residuals for use for the production in primetime and syndication. SAG national executive secretary Chester L. Migden said the new contracts are " an attempt to drive a further wedge into the group that is causing the strike" (i.e., the producers).

Between Monday and Wednesday, 25 such contracts for feature films were signed by various producers, including Mel Brooks and Francis Ford Coppola, said SAG spokesman Kim Fellner. "This is an indication to us that the film makers, the people who actually make the films, have no problem with what we're asking for, It's the conglomerates who have the problem."

So far, Universal has laid off 3,000 employees, according to Joe Hiatt, vice president of MCA Inc. and general manager of Universal City Studios. "Ordinarily, at this time we'd have 6,500 people working for us. We would have hired another 3,300, so that's where the swing lies. We've ground to a standstill." Other major studios report layoffs ranging from "substantial" to "massive." A spokesman for the International Alliance of Theatrical Stage Employes said 15,000 of IATSE's 25,000 members have been laid off. "I'd say that about 80 percent of what we call production people are out of work because of the strike," he said.

Meanwhile, SAG's banning of its members from promoting completed TV and film projects is having far-reaching effects. ICPR, one of Hollywoods largest public-relations agencies, has cut back to a four-day work week, resulting in a 20 percent pay cut to its employes. "They're doing that so they don't have to fire people," said Mac St. John, the business representative for the Publicists Guild. St. John estimated that unemployment among publicists is currently "about 30 percent."

Warren Cowan, president of the Rogers and Cowan public relations agency, called the SAG ban "immoral if not possibly illegal. We have clients in pictures already made. At the time they signed to do those pictures, they agreed in contract to help promote them," he explained.

"By definition we're being affected," said Jeff Berg, a spokesman for Internation Creative Management, a talent agency with more than 2,000 clients. "Our agents are not actively negotiating talent deals," said Berg, adding that so far, there are no plans for layoffs or a four-day week at his company.