Commissioner Pete Rozelle of the National Football League opened the door yesterday to the possibility that he might speak to the Washington Redskins about running back John Riggins' offseason drinking incidents.

Rozelle, speaking in a conference call with writers from around the country, responded to questions on subjects ranging from drug problems in the league to the decline of television ratings to the antitrust suit filed by the U.S. Football League.

Asked specifically about Riggins, Rozelle said, "In Riggins' case, we haven't established the fact that he has a serious problem (with alcohol). What we will do, will be done privately."

Sources indicated Rozelle's interest was not likely to take the form of direct intervention, as in testing for alcohol levels in blood. Rather, it was believed Rozelle might speak privately to the Redskins about Riggins.

Also, sources said the Redskins expressed their own concern about Riggins before they signed him to a one-year contract believed to be worth $825,000. The final stage to his signing was a meeting with Coach Joe Gibbs Sunday in Carlisle, Pa., and it is believed that Riggins' recent arrest on a drunk in public charge and his behavior at the Washington Press Club's Salute to Congress Dinner on Jan. 30 were discussed. Sources said the team will not require him to be tested, but that there was an agreement on the subject of drinking, the details of which were unavailable.

Rozelle touched upon numerous subjects in the hour-long conversation:

*On drug abuse in the NFL: "It's still there, obviously, (but) it has decreased. We have no basis for saying that. It's just our feelings in talking with clubs and players . . . We're keying more on outpatient care . . . (Drug abuse) is something you don't get cured from. It is something where you have to get the guts to abstain. (The outpatient program) is something that we have been working on with the clubs and on our own.

"We think that that's the key for those to get it in an effective state of remission and to refuse to touch the stuff."

*On lower TV ratings in 1984: "I think our ratings have bottomed out. I think we'll see them bouncing back through the last two years of the current television contract (which expires after the 1986 season). We've had cycles before when the ratings have declined, and I think that's what we have here.

"I don't say that we're going right back to '81 levels (all-time record high), that would be pretty difficult. But I think you'll begin to see the ratings start up again this season."

*On the $1.3 billion antitrust suit filed by the USFL, enjoining the NFL from appearing on all three networks: "I had four days of depositions last week . . . Our feeling of course is that the suit is baseless, but that we have to treat it seriously because they are talking about us giving up one or two networks and $1.3 billion in damages. So, you can't treat it frivolously."

On league officiating: "I've been pleased. I have been upset with the so-called 'phantom calls' that you hear coaches talking about. Of course, they bother us as much as anyone else. You look at the film and you see it just wasn't there. It appeared that way, but it wasn't. But in officiating, you'll always have problems with that . . . You have that human element involved.

"The big thing (in rule changes this season) is a new interpretation of pass interference. The new interpretation will be fewer pass interference penalties and a clearer definition for officials on whether to call them or not."