Mayor Diane Feinstein didn't look like a politician facing a recall election. She couldn't stop smiling Thursday after it was announced that San Francisco had been selected as the site of the 1984 Democratic National Convention.
In fact, the city's capture of the biggest plum in the convention business just about blew away the small cloud that tomorrow's recall vote had presented on the mayor's political horizon. Polls had already indicated she would handily deflect the attempt to oust her.
San Francisco beat out Chicago, Detroit, New York, and Washington, D.C., in bidding for the Democratic convention, which brings with it more than 5,000 Democratic delegates and alternates. Those delegates, their families, other party officials, and the usual media swarm are expected to swell the numbers to around 20,000.
Some have come up with the ''estimate'' that the convention throng will spend around $35 million in the Bay Area, giving a big boost to a tourist industry that has slumped in the last couple of years.
In addition, civic leaders expect the convention to be one enormous advertisement for the city as a tourist attraction and for its new Moscone Convention Center.
Despite Detroit Mayor Coleman Young's disparaging remarks about San Francisco after his last-minute flurry of lobbying failed, the ''City on the Bay'' was the front-runner all the way. Democratic National Chairman Charles Manatt of Los Angeles and US Rep. Tony Coelho (D) of Merced, Calif., chairman of the selection committee, didn't mute their enthusiasm for San Francisco, the only Western city in the running.
The Democratic ticket hasn't ''won the West'' since Lyndon Johnson's 1964 landslide defeat of Barry Goldwater (nominated in San Francisco's Cow Palace by the GOP).
Congressman Coelho, who is also chairman of the Democratic Congressional Campaign Committee, said the party ''is telling President Reagan that we are going raiding in his home territory.''
Mrs. Feinstein, who took office when Mayor George Moscone was assassinated in 1978, and who won a four-year term in 1979, faces an exciting two years of politicking. She has mobilized an impressive counterattack to next week's recall attempt and should be an overwhelming favorite for reelection in next year's regular mayoral election.
Next year she will be hostess to the Democratic National Convention, and some observers speculate that Mayor Feinstein, who expects to be a Mondale delegate, could emerge as the nation's first woman to become a vice-presidential nominee.
San Francisco will spend some $8 million for the privilege of hosting the convention, mostly for alterations and improvements to the convention center and for security. Detroit's Mayor Young made much of the fact that the city has a small police force (1,971 members). As many as 2,000 extra officers will be brought in from nearby cities to ''work'' the convention.