Mike Baker of Arlington, Va., ran afoul of his first left-handed opponent tonight, Maurice Hope, world junior middleweight champion, and failed in his attempt to win Washington's first boxing title in a decade.

Hope, a small mild-mannered Antisuan version of Apollo Creed in the movie "Rocky," had little trouble with Baker, scoring a technical knockout in the seventh round at Wembley Arena.

The champion floored Baker with a right to the chin followed by a left to the midsection one minute into the seventh round and then pummeled the challenger all over the ring before referee Raymond Baldeyrou of France stopped the fight with 2:20 gone in the round.

Although Baker failed to bring back the title, Washingtonians may get the chance to see the champion fight at Capital Centre early next year. Terry Lawless, manager of Hope, is trying to line up a title bout with Sugar Ray Leonard, whom the British expect will be welterweight champion by then.

Hope, who was hardly tested tonight, showed he is a solid puncher; but he does not possess Leonard's speed. Leonard, still able to make the welterweight limit of 147 pounds, would have to give several pounds away to the champion of the 154 pounders.

Baker, 27, never could get untracked against the left-handed Hope and admitted after the fight that he had difficulty because he had never faced a southpaw before. His trainer, Jim Ed Jones, also of Arlington, said he hopes to line up a few more fights for Baker before the end of the year against left-handers to gain more experience.

Since the fight did not go the distance, the score cards of the referee and two judges were not disclosed under British rules but, at best, Baker only won the third round and split the first and fourth. Hope started slowly but from the fifth round on the fight was all his.

Hope's awkward right jab kept Baker off balance early in the fifth and then suddenly the champion opened up with a series of five straight rights halfway through the round without retaliation. Staggered, Baker attempted to clinch but Hope kept him at bay and near the end of the round got in a barrage of lefts with Baker again covering up and not returning the blows.

Baker backpedaled throughout the sixth and managed to stay out of trouble only to run into disaster in the seventh. A right cross to the chin put Baker down for the mandatory eight count and after that Hope swarmed all over him, never letting up as he bore in for the kill.

The game Baker fought back with a flurry of lefts and rights at midring but Hope just kept moving in and trapped Baker in his own corner. Hope bounced Baker off the ropes and was hitting him at will when the referee stepped in and ended the bout.

Unmarked after the fight, Hope said he would like to have another title fight before the end of the year. His manager said he hoped to line up Leonard early in 1980 and added he wouldn't try for the bout unless he thought his man could win.

Baker, both eyes puffy and one bleeding from an uppercut in the first round, said he did not think the referee should have stopped the fight but admitted that on this night, at least, he was outclassed.

Sponsored by Washington lawyer Edward Bennett Williams, Baker has three wins and two losses at Capital Centre in his 35-12-1 record. He was attempting to become the first Washington-area world champion since Bobby Foster held the light heavyweight title from 1968 to 1974.

Hope, 27, a resident of the Cockney area of London, has won 25 of his 27 bouts.