President's address fell on many darkened TVs in L.A.

If a tree falls in a forest and no one hears it, did it make a sound? If the cosmopolitan denizens of these sidewalks are any indication, then the President's State of the Union address Wednesday night was a tree that landed like a leaf fluttering to the ground.

The President's message hit the airwaves on all three networks, complete with long rebuttals and analysis sessions afterward. But most of the dozen people encountered on the sidewalks here Thursday morning missed it completely.

''Didn't get home from work until 8 o'clock,'' says a young accountant wearing a gray suit. But he would have watched if he had been home earlier . . . ''probably.''

His response was a common one. In fact, since the President's speech started at 6 p.m. on the West Coast, many people apparently didn't get home in time. Some caught only the Democratic rebuttal afterward.

''I saw the end of the Democrats and didn't understand what was going on,'' said a printer, waiting for a bus.

Would he like to have heard the speech?

''I could take it or leave it.''

Some saw the evening's whole presentation. A pinstriped banker, interviewed at a brisk clip, calls himself a strong supporter of the President, thought Reagan's portrayal of the State of the Union was accurate, and the Democrats' response ''ridiculous.''

''I could grab 20 people off the street who agree with me and make myself look good,'' he says in disparaging the Democratic presentation.

Is he as upbeat about the nation's progress as is the President? ''Well, there's a lot that still needs to be done, but the President is doing the right things.''

But the banker was an already-convinced Reagan supporter.

A young woman waiting for a bus with a copy of Mademoiselle magazine under her arm, an assistant buyer at a department store, only saw part of the speech, but she was surprised by it.

''I was surprised by how much I disagreed with, since I don't know much about his policies.'' She disagreed most strongly with the President's support for prayer in the schools.

A crisp young man in trendy, casual clothes - he teaches ''movement'' - was almost disdainful of the whole matter. ''I'm not political at all.''

A well-dressed woman with a South African accent, discreetly holding up Jehovah's Witness literature, had much the same response. ''I have no interest in politics, so if I had been home watching TV, I would have just turned to something else.''

At Jerry's Rolling Chef lunch truck, mariachi music playing inside, Jerry pleaded the rigors of working life: ''I don't have time for to watch TV.''

''I didn't know he (Reagan) was on last night,'' admits a young Latina woman. ''I didn't watch TV at all.''

And a young fellow from Japan who works as a cook and jack-of-all-trades at a boarding house saw part of the speech before he had to go to work. He likes President Reagan, he says in eager but halting English, but the speech went a little too fast for him to understand.