Like the best guests, they arrive on time, do not overstay their welcome, prove very entertaining and have good manners. Betty Comden and Adolph Green romp and stomp through some of their collected works for the American musical theater tonight on "A Party," second special in the Mobil "Summershow" series, at 8:30 on Channel 5.

Comden and Green, lyricists and scriptwriters, have been performing their own numbers on vitrually any sage that would have them for years. They did some of this material on a Previn and the Pittsburgh" PBS show with their old chum Andre Previn last year. "This is actually a celebration of the fact that we can still get up and perform," Comden explains near the start tonight's program, videotaped with only piano accompaniment at the John Drew Theater in East Hampton, Long Island.

Some of their comedy numbers, including a operetta spoof they sued to do at the Village Vanguard, have aged severely. But their best work, that written in collaboration with composers Leonard Bernstein or Jule Styne, has the kind of snappy, crackly New Yorkishness and a steal of merriment that have now vanished from Broadway. Not even Comden and Green can really do it anymore, as a couple of tunes from their most recent effort, the insignificant "On the Twentieth Century," demonstrate.

Highlights are innumerable and include "New York, New York" and "Some Other Time" from "On the Town"; "100 Easy Ways to Lose A Man," "Ohio" and "The Wrong Note Rag" from "Wonderful Town"; "Never Never Land" from "Peter Pan"; "Make Some Happy" from "Do Re Mi"; and, from "Bells Are Ringing," "Just in Time" and "The Party's Over."

Not all the material is exemplary, but Comden and Green, especially Green, tear into it all with such fervor and relish you'd think they were still doing a backer's audition and had never had a hit. When not singing, Green looks like a wealthy investment banker who is one of Di-Gel's better customers. When singing, Green looks like a wealthy investment banker who is one of Di-Gel's better customers but who just loves to sing.

Clark Jones directed, shyly but efficiently, and the pianist is Paul Trueblood. In the first act, Comden wears a blue dress and Green a matching blue tie. In the second, Comden wears a red dress and Green a matching red tie. And when they sing such inquiring lines as "Where's the real stuff in life to cling to?" they give every appearance of knowing the answer.