WPKX-FM (105.9), which once was the most popular country music station in the area but lost its prominence in the ratings over the past two years, yesterday changed its call letters to WCXR and its format to "Washington's classical rock."

The switch leaves the area with one principal country station, WMZQ-FM (98.7), and a plethora of stations that play some type of rock 'n' roll.

The new format, said station President and General Manager William Sherard, is designed to serve "disenfranchised" listeners in their late twenties and thirties. "After we installed our new signal, we decided to take a fresh look at the Washington market," Sherard said yesterday. "It said a large group of adults between the late twenties and thirties found some rock stations too hard, some stations too wimpy and some stations quite frankly too repetitive. It also pointed out that there was a huge area of core music that these people continued to purchase and had in their libraries that wasn't being served in the market."

In some markets, said Sherard, the programming he's talking about is called "The Big Chill" format. "The classic rock format is more than just a museum on the air. We will also play the songs we have determined will be the classical hits of the '80s, like Phil Collins," said Sherard. Since the station's new antenna was installed Dec. 20, he said, permitting greater penetration of the Washington area, two music preference surveys showed that the "disenfranchised" listeners want to hear more from Bob Dylan, Chicago, Foreigner, the Doors, the Kingsmen and Little Richard. Yesterday at 1:05 p.m. the old KIX played "Adios Amigos" and the new WCXR debuted with "Light My Fire."

Sherard, a member of the Country Music Association board of directors, said the change doesn't signal a downward trend in country music's popularity. But both major country stations suffered considerably in the last Arbitron Ratings survey, with KIX garnering its lowest ratings in years. "I don't think country music is dead by any stretch of the imagination," Sherard said. "It is going through a transition. Because there are so many choices for listeners, people who are secondary listeners simply are not going to country. But the core is there."

Frank Byrne, general manager of WMZQ, agreed that the country audience was still strong and added that the demise of the old KIX would hurt the local market. "We think one of the things that makes a great radio station is good competition, and there was no more heated a competition than between WMZQ and KIX. That competition provided motivation for the best of us to be the best we could be. We have to provide our own competition and that will be even tougher."

KIX, which had a more hard-core country playlist, had been attracting 250,000 listeners per week; WMZQ, which has a more pop-oriented country playlist, has 335,000 listeners per week. WMZQ plans a major advertising campaign Thursday to welcome the homeless KIX listeners.

WMZQ began to overtake KIX, which is owned by the Cleveland-based Metroplex Co., in the spring of 1983. Most observers believe that the downswing of KIX intensified with the short-lived addition of controversial deejay Gary Dee to its lineup in 1983 and continued with the $1 million television advertising campaign of its rival WMZQ in 1985. Dee, who specialized in insult humor primarily directed at homosexuals, women and ethnic groups, worked for the station from October 1983 to March 1984.

Rivals who were monitoring the new station yesterday did not expect WCXR to duplicate much of their format. Bob Hughes, program director of WLTT-FM (94.7), said, "Our listeners turn to us for light rock, about 50 percent of our songs are old, and our major audience is women. In this age of specialization, radio is doing what magazines have done for a long time. I think there is room for rock aimed at males." A spokeswoman for WWDC-FM (101.1), which plays album-oriented rock, has a large male audience and is considered by Sherard to be one of WCXR's targets, would not comment yesterday on the new station. Bill Dalton, the general manager of WXTR-FM (104.1), until now the only all-oldies station, said, "From what I have heard they are not playing too much of our songs, not more than anyone else does. Some of the stations in town have positioned themselves so that it is very hard to define what they are to someone else. I am surprised WCXR jumped into the same pool."