UPDATE 2-John McCain speech draws record TV ratings

(Adds overall figures for Republican and Democrat conventions)

By Jill Serjeant

LOS ANGELES, Sept 5 (Reuters) - Republican presidential candidate John McCain beat Democratic rival Barack Obama in the crucial battle to attract U.S. television viewers during their race to the White House, according to figures released on Friday.

Nielsen Media Research said a record 38.9 million TV viewers watched McCain accept the Republican nomination on Thursday, slightly more than the 38.3 million people who tuned in for Obama's speech last week.

McCain's tally was believed to be the biggest commercial TV audience every for a single night of a U.S. political convention, Nielsen said.

The Republican convention in St. Paul also attracted more average viewers overall than the Democratic Party convention in Denver last week.

McCain, 72, trails Obama only slightly in most national opinion polls as they head into the Nov. 4 presidential election that will make history either by putting the first African-American into the White House, or choosing the first female vice president.

Nielsen said an average 34.4 million people watched the Republican convention over its main three days. The convention was scaled back on it's opening day as Hurricane Gustav made landfall on the U.S. Gulf Coast.

An average 30.2 million viewers tuned in to the four-day Democratic Convention in Denver, Nielsen said.

McCain had the daunting task of following his surprise pick for running mate -- little known Alaska governor Sarah Palin -- who had fired up the convention a day earlier with a feisty speech hitting back at critics who questioned her credentials for the job.

Some observers had worried that Palin might upstage McCain, whose reception inside the convention center in St. Paul was more muted than the cheers for the self-described "hockey mom" and mother of five.

Palin's national prime-time TV debut on Wednesday was watched on television by 37.2 million Americans.

McCain touted his credentials as a reformer and portrayed himself as the real agent of change in the race against Obama as he accepted his party's presidential nomination in an arena filled with supporters waving blue "Country First" signs.

"I don't work for a party. I don't work for a special interest. I don't work for myself. I work for you," McCain said in a speech that included only passing criticisms of Obama after a convention marked by scathing attacks on the Democrat.

Eight U.S. TV networks carried McCain's speech live during prime time.

With the conventions and the selections of running mates out of the way, the next big milestone in nationwide audience terms is the first of three presidential debates, on Sept. 26 in Oxford, Mississippi.

By comparison, 34.9 million U.S. television viewers watched the opening ceremonies for the Beijing Olympics in August and talent show "American Idol", the most watched TV show in the nation, averaged 28.1 million viewers last season.