The trial to determine whether the National Football League can block the Oakland Raiders from moving to Los Angeles Memorial Coliseum got under way today at U.S. District Court, and from the start it was clear that the key issue will be the big-time business of professional football, a subject the NFL hierarchy does not enjoy discussing openly.

Even while the court battle got under way, negotiations toward a possible out of court settlement continued and it was reported that at least one member of the Coliseum commission was prepared to dump the deal with the Raiders in exchange for getting an NFL expansion club for Los Angeles.

At the request of Judge Harry Pregerson, both sides have hired Los Angeles attorney Robert M. Loeffler to act as an intermediary in settlement discussions. But neither side holds out much hope for the effort.

An attorney for the Coliseum, which filed the antitrust suit against the NFL in 1978 when the Rams announced they were moving to suburban Anaheim, made his opening remarks this morning and was followed by an attorney for coplaintiff Al Davis, managing partner of the Raiders.

Coliseum attorney Maxwell Blecher told the jury of seven women and three men, chosen for their indifference to pro football, that nothing less than the American free enterprise system is at stake in this trial.

"When we lost the Rams, we didn't cry," Blecher said. "We did the redblooded American thing. We went out and got ourselves a team. But they (the NFL) won't allow us to have it."

At issue is Rule 4.3 of the NFL constitution, which states that a club cannot move outside its city without the consent of three-fourths of the other 27 team owners. The owners have voted down Davis' request to move to Los Angeles.

The Coliseum and the Raiders argue that Rule 4.3 unreasonably restrains trade in violation of Section 1 of the Sherman Act.

In his opening remarks, Judge Pregerson told jurors the key question they must decide is whether the NFL is a single enterprise, as the league contends, or 28 separate and competing teams, as the plaintiffs argue.

Blecher, anticipating that the league will argue that Oakland fans would be the real victims if the Raiders moved to Los Angeles, sought to put the case strictly in economic terms. "They will have to make adjustments just like the Rams fans had to," he said, suggesting that Raider fans should switch their allegiance to the San Francisco 49ers.

Davis' attorney, former San Francisco mayor Joseph Alioto, portrayed his client as a hostage of the Oakland coliseum. He said that the Nfl Rule 4.3 has undercut Davis in negotiating for financial incentives from city officials there.