Leon Spinks, sitting high and dry with a suddenly discovered - at least suddenly reported - rib injury, could be leaving the lot of them to thrash around, but:

It's everybody into the shark-infested heavyweight boxing pool with yesterday's goodbye kisses to retirement by not one former world champion, but two.

Joe Frazier, 34, will come back with an April 15 bout against Gerrie Coetzee in Johannesburg, according to South African promoters. And ABC-TV will be there.

George Foreman, 30, will return to the ring, he declared in Houston, "for the sole purpose of manifesting Jesus. 'I've asked God for a chance to do it again to exalt Jesus." His first comeback match hasn't been announced, but you can bet ABC, or CBS, or NBC will be there.

All this before the last word came in last evening from sportscaster Brent Musburger, who works for CBS:

"I've learned that the newly crowned champion injured a rib cage cartilage prior to his upset victory last month in Las Vegas over Muhammed Ali. The injury was aggravated during the Ali fight and medical advisors are prescribing rest." Probably to September or October. Indubitably costing Ken Norton has promised May shot at Spinks . . .

The word from South Africa that Frazier will fight Coetzee, that country's champ who is white, seemed almost in reply to ex-champ Ali's recommendation that black U.S. group lay off and let the South Africa-United States Davis Cup matches go on in peace at Nashville on March 17.

"If we open our arms and show love and affection," said Ali, "they got hearts, it's possible that they will feel bad and start straightening up over there, too . . ."

Re network power (Ali's Davis Cup remarks came at the end of his Saturday fireside chat pleading for a rematch with Leon Spinks before the new champion fights Norton, Bob Arum and Butch Lewis to Top Rank, Inc., are due in San Diego today to meet with Norton's manager, Bob Biron.

Here's what they were saying - before the Spinks injury blockbuster:

Lewis insisted he will not try to buy off Norton to clear the way for a richer Ali-Spinks rematch - "even though it's economically foolish for everyone but CBS.CBS is stealing the fight." (That network has a $1.55 million contract with Top Rank for Spinks' first defense against anyone but Ali).

Biron, for his part, criticized CBS for giving Ali a half-hour of air time. He suggested collusion between CBS, Top Rank and Ali and a questionable dual ole by CBS as medium and promoter and warned, "Congress is going to look very seriously into the situation of CBS' activities relating to promotion and control of fighters" . . .

The NFL Players Association, reporting its recent seminars in Fort Lauderdale and Baltimore made a hit with "more than 65" agents who attended, will go ahead and organize ARPA immediately. ARPA is Association of Representives of professional Athletes, to govern conduct of lawyers and agents in a number of sports. Ed Garvey, NFLPA executive director, said from HQ here the governing board will be made up equally of agents and of representatives of various player associations. By golly, Garvey reported, "Most of the agents wanted even more stringent rules than originally proposed . . . Agents will have to agree to abide by the code of professional ethics and constitution and to provide full disclosure of fees, services and clients, in order to join," (and be listed in an ARPA directory). The concept will be reviewed by agents and lawyers (more than 400 are active in the field) at two more seminars, this week in San Francisco and June 8-9 in Chicago . . .

Yesterday was Bob Beathard's first in the Redskin Park office as general manager, but the signing of free-agent defensive linemen Ron Pruitt (Nebraska, flunked Bills) and Stan Varner (Brigham Young, flunked Falcons and Rams) had been arranged before his hiring . . . Let's hear a last hurrah for Buckpasser. The 3-year-old horse of the year 1966 (even though he didn't run in the Kentucky Derby) become a top sire since syndication in 1967 has died at Claiborne Farm, Paris, Ky. Ruptured aorta at age 15; he'll be buried in good company at Claiborne's thoroughbred cemetery, and if there's a plague it'll no doubt tell you he won 25 of 32 starts and earned $1,462,014 . . . The theft of 46 Mets shirts from St. Petersburg training camp Saturday and 25 Phillies shirts from Clearwater, Fla., the day before is reported solved by Fort Lauderdale police. A detective arrested - in the Yankees' clubhouse - Warren Winkler 33, of North Hollywood, Calif. Said an officer, after Winkler was jailed on stolen property possession charges, "He has lined the walls of his home with sports memorabilia."