FORMER RADIO GIANTS KROQ, KOST PLUNGE IN LATEST ARBITRONS.

Byline: Fred Shuster Daily News Staff Writer

Modern-rock KROQ-FM (106.7) and soft-hits KOST-FM (103.5) are apparently the latest victims of the war of attrition local radio stations are fighting.

Arbitron ratings figures released Friday suggest the stations that assumed the alternative-rock music mantle in the last few years - KLOS-FM (95.5), KSCA-FM (101.9) and KLSX-FM (97.1) during weekends - have chiseled away at KROQ's core audience, leaving the influential Burbank new-rock outlet to drop from No. 6 in the winter to No. 10 with a 3.3. percent share in the current spring report.

KOST's spring plunge from fifth to 11th place with a 3.2 percent audience share hints that more soft-hits fans than ever before are sampling smooth jazz KTWV-FM (94.7), oldies KRTH-FM (101.1), hot adult-contemporary KYSR-FM (98.7) and soft-rock KBIG-FM (104.3), all of which showed improvements.

Meanwhile, Latino radio continued to dominate the market overall. KLVE-FM (107.5), which broadcasts romantic ballads in Spanish, maintained the top spot for the third consecutive quarter in both mornings and throughout the day.

The station - known as K-Love - ranked first with a 7.2 percent audience share. Pepe Barreto drew a 7.6 share to top the all-important morning derby.

Also in mornings, r&b outlet KKBT-FM's (92.3) ``John London & the House Party'' jumped from third in the winter to second-place and a 5.3 percent share of the audience in the spring. Talk-radio KLSX-FM's (97.1) Howard Stern placed third with a 4.8 percent share, followed by hip-hop radio KPWR-FM's (105.9) Baka Boyz, who came in fourth with a 4.5 percent share.

KRTH enjoyed perhaps the period's biggest daytime ratings leap, from 10th in winter to No. 5 and a 3.8 share in spring. The oldies station, whose unusually strong signal reaches from Baja to Santa Barbara, also placed first among English-language stations in the hotly sought-after 25-to-54 age demographic.

``Consistency pays off,'' said Pat Duffy, KRTH's vice president and general manager. ``The station stayed solid, and the other stations jockeyed around us. If we just do what we do, we'll always be solid in the market. We work hard to present a contemporary-sounding station that just happens to play oldies.''

The spring Arbitron survey of listeners age 12 and older is conducted by mail and covers the period March 28 through June 19. Each share point equals about 17,000 listeners.