For the third time in 10 years, and the first time during the middle of a season, major baseball league players have laid down their bats and balls and gone on strike.

Marvin Miller, executive director of the Major League Baseball Players Association, announced the strike early this morning.

It became effective at 2:30 p.m. Eastern Daylight Time, the scheduled start of today's game between the Chicago Cubs and the San Diego Padres.

Representatives for the owners and the players met again this morning but, as expected, the discussions were to no avail and no new proposals were presented.

After meeting with the owners' representatives for 30 minutes, Rusty Staub, the New York Mets' player representative, said, "I wish I could say something positive, but I can't. There is a total roadblock."

Federal mediator Kenneth E. Moffett agreed: "They're pretty deadlocked." Moffett said he would renew negotiations Monday or Tuesday.

The players went on strike for 13 days in 1972 over their pension plan and for eight days during 1980 spring training over free-agent compensation, the issue that caused this strike.

Although none of the parties would predict how long the strike might last, one source close to the negotiations said it could continue the rest of the season.

The games missed will not be replayed, according to a spokesman for Commissioner Bowie Kuhn. The commissioner, who has not taken part in the talks, also said today he will try to help the negotiators find an "early solution."

The philosophical chasm separating the owners and the players was evident in the remarks of Ray Grebey, the owners' chief negotiator, and Don Fehr, general counsel of the players' association.

Grebey outlined the areas of disagreement, saying, "The first is in the area of the level of compensation for a ranking free agent . . . The second is who pays the compensation . . . And third, the players still object to the fact that the signing of a qualify fre agent triggers compensation by the club that signs him."

But, he added, "The 26 clubs feel this is an unnecessary strike . . . It's a minor adjustment in one paragraph in the free agency clause, which does not deal at all with the question of free agency but of compensation. It is not a strike issue."

Fehr responded, "What their proposal would do by changing a few small lines [in that paragraph] is change the dynamics of [salary] negotiations. It'll produce a backward movement in salaries, player mobility and bargaining power. If it weren't a strike issue, I suspect they wouldn't have procured $50 million in strike insurance last year."

The owners, who took out the insurnace with Lloyd's of London, will not begin collecting for 13 days of 152 total games. Once the policy is in effect, Major League Baseball will reportedly receive $100,000 per game per day for 500 games. At that rate, the insurance should last through about Aug. 1.

The owners also have a mutual assistance fund reportedly close to $15 million to cover from the start of a strike until the insurance coverage begins.

Peter Leitch, president of Reed Stenhouse Inc., the owners' insurance broker, refused to comment on whether the insurance would be jeopardized if the owners are found guilty of an unfair labor practice charge.

The hearing on the charge is scheduled to begin a week from Monday before a National Labor Relations Board administrative law judge. Relations Board administrative law judge. Questions have been raised about whether the owners would have to give the players back pay if found guilty.

Sources close to the NLRB said normally an employer does not have to give back pay in such a case. However, if the employe makes an unconditional offer to return to work and the employer unlawfully refuses to take him back, the employer would have to provide back pay from that date.

This usually happens when an employer replaces employes with other workers, and is an unlikely scenario for baseball.

In Washington, the NLRB said it would not have a decision today about appealing the U.S. District Court ruling denying the NLRBs request for an injunction to prohibit the owners from implementing their free-agent compensation plan until next spring.

During meetings Thursday, the owners made what Grebey called "some suggestions in the areas the players have been concerned about."

The owners' compensation plan says a team signing a free agent in the top 50 percent of all players must provide another player to the team that lost the free agent.

A team losing a player in the top third of players at his position could select the 16th player from the roster of the team signing the free agent. A team losing a player in the top half of his category would be able to take the 19th player from the team signing the free agent.

Fehr said the owners offered to modify the proposal to include the top 40 percent of players instead of the top 50. But the compensation for free agents in the top third would still be the 16th player, and compensation for the others would be the 19th.

Sources say the owners also offered a variation on the players' pooled compensation proposal. The owners reportedly proposed having each team that signed a free agent put 25 players into the pool. The team that lost a free agent would select a player from that pool.

Grebey said these proposals were still on the table, although the players have dismissed them as inadequate. "They're basically still saying, 'You've had our proposal for 18 months, just take it.' That's why there's no baseball being played today," Fehr said.

The players also proposed a variation on their pooled compensation plan Thursday, suggesting each team choosing a quality free agent designate four players from its 40-man roster for the pool. A team losing a free agent could select either a player or an amateur draft choice.

Previously, the players association had suggested that all clubs contribute an unspecified number of players to the pool.

Asked if the players' latest proposal had been withdrawn, Fehr said, "Not yet."

Sources familiar with the negotiations said that often when a strike is called, all proposals are withdrawn. But parties may not want to do that here, because it could harden positions and jeopardize chances for a quick settlememt.

Bob Boone of the Phillies, Steve Rogers of the Expos and Doug DeCinces and Mark Belanger of the Orioles, have been designated as the players' negotiating committee.

Last week, Marvin Miller, executive director of the players association, said he would excuse himself from the negotiations if a strike occurred, because some owners have felt he was the major obstacle to a settlement. Then, Thursday night, Miller said Grebey didn't want to bargain with the players.

Grebey said the charge was "a lot of hogwash."