IT'S SUNDAY night at Gallagher's Pub on Connecticut Avenue. Open-mike host Steve Erwin confronts the microphone with his legs planted firmly, a little apart, like someone bracing for a fight. He begins pounding out a strong, punchy rhythm on his battered-looking guitar, gradually accelerating the tempo. And as his remarkably agile voice soars above the clink and clatter and general din of the crowded bar, people quiet down to listen. The show's begun, and it's the music they've all come to hear. The wry lyrics to "Born a Tourist," a song Erwin wrote 10 years ago, soon have the audience rapt:

"Life's so hard when you're born a tourist

'Cause no one speaks English these days.

I came into this earth in a Hawaiian shirt,

And I'll probably leave that way."

This song, typical of those by the 34-year-old composer, is a curious but effective combination of gritty blues and almost operatic figures, delivered with startling glissandos and occasional pitch-perfect falsettos. It's a vocal style honed during some 16 years of performing, one Erwin says was strongly influenced by a five-year stay in Chicago, where he lived between 1976 and 1982, before returning to Washington. "They had a very different kind of showmanship there from what we have here," he recalls. "Almost a cabaret approach. The musicians were total entertainers, and I learned a lot from them."

You can hear Erwin's compelling original tunes, and those of many others at Gallagher's, where Erwin alternates hosting the Sunday open mikes with the local band Back to Back.

In the audience are many other Washington singer/songwriters waiting to perform, among them Sara Landymore and Kevin Jones. These two Gallagher's regulars also play at many of the other showcase bars around town: the Round Table on Wisconsin Avenue, Durty Nellie's in Bethesda, Food for Thought near Dupont Circle and Whitey's and Fin's Bar and Grill in Arlington -- to name but a few. At these events you'll find all kinds of excellent original music: jazz and blues, folk and bluegrass, hard and soft rock and even vocal doo-wop.

The songwriting business is a tough one. It's a rare few indeed who attain the success of a Mary Chapin Carpenter or an Emmylou Harris -- both of whom began their performing careers here in Washington. Open mikes provide a valuable forum for songwriters to try out their material. Jones, who works two day jobs, waxes philosophical about his songwriting.

"Besides being, potentially, income, it's an outlet," he says. "Writing is therapeutic, for one thing, because it gives you something to say back after the grind of working all day. You write and sing to release yourself. It's a thing you dream with."

The 31-year-old Ohio native's dreams have begun to pay off. Over the last several years, Jones has opened shows at the Birchmere some 13 times, for big-name performers such as Doc Watson, Jonathan Edwards, Steve Forbert and John Sebastian. Last year he taped his first collection of songs.

Jones says he looks on the bar gigs as "good practice for when I get the better jobs."

Landymore, 30, is a relative newcomer to the local music bar circuit. "I always knew that I wanted to be a songwriter since I was about 9 years old," she says. "But it's not something you go to college to learn. So I kind of forgot to go to college. But I just continued to write and to play until I got my current job at the Prince William Journal as a police reporter."

Landymore says that over the last year or two she became an "open-mike junkie," appearing at four or more such events per week. She began performing publicly about two and a half years ago. "A friend of mine told me about the Gallagher's open mike," she recalls. "I was a little hesitant about going. And I was real nervous the first time. I didn't think my stuff would go over very well at a noisy bar. So I was really surprised with the reception I got at Gallagher's.

But Landymore's reception at most clubs in town is warm, and she's a favorite of the Gallagher's audience. Her songs are intensely personal, hymns and ironic ballads about love and rain and lonely rooms:

"Stay home, stay away and leave me to my room,

I have an attic now where I sing at night, just like my mockingbird on the roof.

Little rooms for little people, and a little piece of sky,

I moved into the city to a house where it don't rain in."

This song, "The Window Room," is often requested at her performances. You can find it on the tape she finished recording last November entitled "A Choice of Days." Like Jones she sells her tapes herself, backstage after performing. So far, Landymore says, she hasn't had any luck with reaching a potential publishing or recording company. But she's been invited to this year's Takoma Park Music Festival in September.

These songwriters take their triumphs where they can find them, and continue to play all over town. As Kevin Jones says, with conviction, "If your craft is good enough, it will succeed anywhere."BYO GUITAR

Open mikes at any of the following spots frequently feature as many as 15 to 25 acts per night, performing anything from one song to a half-hour set. Musicians generally sign up on a first-come, first-performing basis, although most establishments have their longtime regulars who show up every time.

DURTY NELLIE'S --

4714 Montgomery Lane, Bethesda. 652-1444. Mondays 8:30 to 12:45.

FIN'S BAR AND GRILL --

2421 Columbia Pike, Arlington. 486-3467. Tuesdays 9 to midnight.

FOOD FOR THOUGHT --

1738 Connecticut Ave. NW. 797-1095. Mondays 9 to 11:30.

GALLAGHER'S PUB --

3319 Connecticut Ave. NW. 686-9189. Sundays 8:30 to midnight.

THE ROUND TABLE --

4859 Wisconsin Ave. NW. 362-1252. Tuesdays 9 to 1:30.

WHITEY'S --

2761 N. Washington Blvd., Arlington. 525-9825. Tuesdays 9 to midnight.