On the sidewalks of Eastern Market Sunday, 11 to 5, you'll find the 23rd annual Friendship House Market Day street fair. One of the oldest such affairs in town, the event attracted nearly 10,000 people last year and raised $10,000 for the nonprofit community service center.

This year's lineup includes free entertainment by Philippine dancers, a jazz/funk/gospel outfit called Osiris, the UDC Jazz Combo and the Marine Jazz Band, and a variety of wandering performers, pony rides and games of chance for kids, plus North Carolina barbecue and Mediterranean food.

Friendship House has been helping poor and low-income people for 81 years, with a daycare center, free clothing store, emergency food center, community education, tutoring and computer education and employment services. A DANCE TO SPRING

If you hurry, you can catch the tail end of International Dance Week, which ends Sunday. As part of its regular bounty of free indoor and outdoor music and dance performances, The Pavilion at the Old Post Office will present appearances by several area dance troupes from noon to 6 Saturday.

The Pavilion's stages are busy virtually every day throughout the year, and some other highlights this month include: "D.C. Live," a variety show of local talent, May 11, noon to 3 at the outdoor bandstand; the Feet First Jazz and Tap Company May 12, at 3 on the indoor stage; the Primary Movers children's dance group begins an afternoon of young performers May 18 at noon indoors. To find out what's happening every day, in and out of the Pavilion, call 289-4224. ORIENTAL SEASONING

A traditional Chinese Lion Dance should get things going with a roar as Asian-Pacific American Heritage Week winds up with a free festival (the seventh annual) May 11, noon to 6, at the Washington Monument grounds.

The entertainment includes dancers and singers from China, Indonesia, Korea, Japan, Taiwan and the Philippines; martial arts demonstrations from China and Indonesia (the Indonesians practice "penchak silat," a form of kick-boxing not often seen around here); demonstration of skills like Chinese sand-painting and kitemaking and Vietnamese spring-roll baking (and eating); and the usual festive scene.

"We do this to give the general public a fun way of getting acquainted with the various cultures of Asia and the Pacific," says spokesman Albert Yee, pointing out that Asians are the fastest-growing segment of Washington's population.

The festival will begin with presentation of the Asian-Pacific American Heritage Award to astronaut Ellison Onizuka (born in Hawaii, of Japanese ancestry), who went up in the first Department of Defense shuttle mission January 24, and is due to go back up in November aboard the orbiter Atlantis. THEY'VE GOT THE BEAT

We've heard of a rock group called the Police, one called the Outlaws, and even one called .38 Special.

But D.C.'s own Side by Side is the only pop band we know whose members wear real revolvers on their hips.

The six blue-shirted, silver-badged members of the soul/funk/top 20 outfit are all D.C. police officers (except for the one in the uniformed division of the Secret Service), and they've been rocking together since 1968, which is longer than most professional rock groups can boast. And lots of kids in D.C. have grown up with them, since the band has been making weekly visits to just about every public school and junior high in the city as part of the police department's "Officer Friendly" public relations and education program.

The group will be blasting out hits by Prince, Lionel Richie and Billy Ocean during National Police Week, May 13-17. The week opens Monday, May 13, at 11, with a memorial ceremony at Metropolitan Police Headquarters, 300 Indiana Ave. NW, followed by tours of the headquarters, a helicopter landing, and demonstrations by the dogs of the K-9 section, and of course, a set by Side by Side. On May 16 and 17, Police Week events will move to Western Plaza, where safety exhibits will be set up; the band will perform May 17 at noon.

Side by Side bass player Sgt. Robert Gross, who has been called the Prince of the Metro police department, has been with the band for 14 years, since he was plucked from directing traffic at North Capitol and I and strapped on a bass for the Community Relations Department. Now he's got what you could call the best beat in the city. Call 727-4283 for information on Police Week events. NOW YOU SEE IT

Prestigious prestidigitators will appear for the first annual All- American Magic Festival, which begins May 18 at 10:30 a.m. sharp on Western Plaza across from the National Theater on Pennsylvania Avenue.

More than a hundred magicians, musicians, mimes, jugglers, breakdancers and other unclassifiable performers will perform on three platforms, not to mention the amateur magic enthusiasts who perform impromptu tricks offstage.

At high noon, local magician Hal Diamond will attempt his first-ever Houdini-style escape -- dangling straitjacketed and upside-down from the 150-foot hook-and-ladder supplied by the D.C. Fire Department. "It will be scary, daring, frightening, gutsy and thrilling -- for me and the audience," says Diamond, whose work has so far been limited to company picnics and outdoor shows with Blackjack the Rabbit (formerly Rabbit Redford), who Diamond has painstakingly trained to do card tricks.

Diamond's been practicing with a straitjacket twice a week, and bought a pair of gravity boots, so he can hang upside down at home. "Thrills are not really my image," he says. "I'm obviously not going into this to fail, but I'm also praying that all my future clients don't expect this kind of thing."

Once his sparkly stage suit has vanished, Diamond reassumes the persona of Harold Henderson, mild-mannered seventh-grade English teacher at Westland Intermediate School in Bethesda, where his students have begun making wisecracks like "catch your act" and "you'll be a hit."

One of the day's dazzlers is sure to be the All-American Slice-a-Thon (11 a.m.) -- the cutups who are organizing the event hope to make a mark in the Guinness Book of World Records for the most people sawed in half at one time. "It's overkill," Diamond says, pun intended. "We'll have three or four guillotines, a couple finger choppers, some bow saws and hacksaws, a couple swords through the neck . . ."

In the evening at 8, the music and magic continue, moving inside to the stage of the National Theater, where five magicians and four singing groups will entertain for free.

The event is being conjured up by the Pennsylvania Avenue Development Corporation and the National Theater's Saturday Morning committee, the same team that concocted last year's 15,000-spectator breakdance spectacular on Western Plaza.

For those who care to prepare for this event, Open University is offering a course on magic beginning this coming Monday. Cost is $20. Call 966-9606 to register. WILD IN THE STREETS

The Magic Fest is followed May 19 by the Hometown Run and Festival, sponsored by the Washington Urban League.

The starting gun for the 15K (that's 9.3 miles) downtown run goes off at 9; the 3K "fun run" gets going at 9:05 a.m. The route starts at the District Building at 14th and Pennsylvania, and travels all over the city. Registration deadline is May 13 for the 15K; cost is $7. For the 3K, register at the starting line; cost is $3. All entrants get a T-shirt.

The races are followed by a free party on Western Plaza, featuring jazz from the UDC Jazz Ensemble and the Lettumplay youth band; comedians and WKYS deejays; and the Wheels of Fortune disco roller skaters. Food booths will be set up by a variety of restaurants from the Shops at National Place.

Proceeds from the run and festival benefit the Washington Urban League's youth service programs, which provide counseling, job training and employment services. Call 265-8200 to register for the races or to volunteer to help with the race.