If Today’s Weather Isn’t Hot, That’s Cool : L.A. Marathon: After two years of warm temperatures, runners figure to get a break and maybe even a shower.

Today’s fifth annual Los Angeles Marathon will feature the usual stampede of runners through city streets, with more than 20,000 expected to start. The usual tiny elite group has been assembled. The usual actors and celebrities will jostle their way to the front at the start, the better to be seen on television.

The one change that could improve the race is the weather. After two years of too-warm temperatures, the forecast calls for the day to be cool with the possibility of light rain. It’s welcome news to the top runners.

“I’m hoping for cool weather. That will help us,” said defending champion Art Boileau of Canada.

Boileau has been able to take advantage of fading lead runners to win here twice. He heads a handful of elite male runners, none of whom appears to be a clear favorite. Boileau has as his incentive the Canadian record of 2 hours 10 minutes 9 seconds. His personal best is 2:11:15.

“I’m not sure of my fitness. I haven’t done much racing,” he said. “But my training has been going well. Last year I wasn’t as fit. I’ll try to run at an even pace, but you can’t let anyone get away from you.”

The two men Boileau overtook to win last year are again in the race.

Gidimas Shahanga of Tanzania faded to fourth after leading through much of the 1989 race. His personal best is 2:09:39, and, like many African runners, he probably will go out fast and make the pack chase him.

Boileau also went past Mark Plaatjes, who was in second place last year until being forced to drop out at 18 miles with severe blisters. Plaatjes has been running in a stretch of bad luck. He was fourth in the New York Marathon last November when he developed hypothermia and dropped out at 21 miles.

“My last two marathons, I’ve been properly trained, and something weird has happened, abstract things I couldn’t control,” he said. Plaatjes’ 2:08:58 is the fastest time in the field. “I haven’t had a bad marathon until last year. I hope I’ve gotten that out of my system.”

Plaatjes calls the L. A. course deceptively difficult but says, given good weather, the field is capable of running a sub-2:10 race.

Soviet runner Vladimir Kotov has one of the field’s fastest times but has also experienced bad luck. Thursday, Kotov was hospitalized with kidney stones. He was released Friday morning, but the painkilling drugs Kotov took while in the hospital are banned and would show up in postrace drug testing. Officials had to get a special dispensation for Kotov, who is expected to run.

Julie Isphording, one of the women’s favorites, has had difficulties here, too. Isphording, from Cincinnati, dropped out of the 1984 Olympic marathon at 11 miles when a tendon in her foot snapped.

“I’m getting another chance (in L.A.),” she said.

Isphording had back surgery in 1987 and has made it clear that her goal is to break 2:30, recognized as the threshold for world-class status. Her best is 2:30:54.

“I’ve been saying that for four years,” she said. “I’d like to do it here. I won’t be heartbroken if I didn’t break 2:30 and I won the race, but I’d like to do both.”

Pushing her will be a handful of runners, all with about the same times. Lizanne Bussieres of Canada, Tatyana Gridneva of the Soviet Union, 1988 winner Blanca Jaime of Mexico and Sylvia Mosqueda of L. A. all will probably be in the lead pack.

“In any marathon, the biggest competitor is myself,” Isphording said. “I try to get myself together and hang on to run negative splits. From Mile 15 to 16, that’s where the pack builds up. The race really begins about Mile 18. That’s when you look around and say, ‘OK, what are we going to do with everyone?’ ”

Isphording said the fitness of the runners and the weather will answer that question.