* This afternoon, a presidential news conference on CNN, C-SPAN, Fox News Channel and MSNBC.

* Tonight, a Martha Stewart holiday special followed by the movie "A Holiday Romance" on WUSA.

* "it's like, you know . . ." returns to the ABC lineup on WJLA.

* And "Unitas" on HBO.

Presidential News Conference

President Clinton holds a news conference live from the State Department in Foggy Bottom (CNN, C-SPAN, Fox News Channel and MSNBC at 2 p.m.).

Awards Show

The 1999 Billboard Music Awards (CC). Live from Las Vegas, a ceremony honoring the top artists and records as determined by this year's Billboard charts. Performances by Celine Dion, Juvenile, Jennifer Lopez, Ricky Martin, Metallica, Red Hot Chili Peppers, Leann Rimes and Britney Spears. Two hours (Channel 5 at 8).

Holiday Special

Martha Stewart's Home for the Holidays: The Family Tree (CC). The domestic empress returns with her third Christmas special. Aretha Franklin performs and bakes a ham, although not simultaneously. One hour (Channel 9 at 8).

Cable Specials

Colin Cowie's Millennium Party. The "style guru" gives advice on how to throw a fabulous New Year's Eve party (Romance Classics, 7:30).

Sesame Street Unpaved. Five original cast members of the fabled children's show look back at its most memorable moments. One hour (TV Land at 8).

Unitas (CC) profiles football legend and former Baltimore Colt Johnny Unitas through interviews and rare footage. One hour (HBO at 10).

Prime-Time Movie

A Holiday Romance (1999) (CC). A school superintendent (Gerald McRaney) is in a pickle when he is asked to slash the music department, which is run by the woman he loves (Naomi Judd). Andy Griffith appears as the super's father. Two hours (Channel 9 at 9).

Newsmagazines

Dateline (CC) reports on a new round of auto crash tests (Channel 4 at 8).

20/20 (CC) interviews entertainer Liza Minnelli and former pro baseball player Billy Bean, who recently came out of the closet (Channel 7 at 10).

Series

Two Guys and a Girl (CC). Johnny and Sharon move into a basement apartment and become building supers (Channel 7 at 8).

it's like, you know . . . (CC). A sexual harassment insurance saleswoman (Mimi Rogers) comes on to Arthur on his first day at the Los Angeles Times (Channel 7, 8:30).

--