These were the Dallas Cowboys and the San Francisco 49ers and the final score was 45-14, which wasn't really surprising.

Unless you consider that it was the Cowboys who had the 14.

"Our team," said Dallas Coach Tom Landry, after a day of windless warmth, always a rarity in Candlestick Park, "was in a fog."

Now, the Dallas Cowboys also are in a slump. Last week they lost in St. Louis, 20-17. Today they were beaten by a team they haven't lost to since 1972 and a team they routed, 59-14, last year.

The Cowboys are 4-2, two games behind the Philadelphia Eagles, who usurped the NFC East title last year. Right now, there is no joy on the prairies.

"We ate humble pie today," said Tony Dorsett, who gained 21 yards on nine carries. This was the worst output for the Dallas running back since Sept. 18, 1977, his first game in the NFL, when he gained 11 yards on four carries.

"Right now, we are two down to the Eagles and we're sliding," Dorsett added after the most one-sided Dallas defeat since 1970 when St. Louis won, 38-0.

The 49ers led, 21-0, after the first quarter. They led, 24-7, at halftime. They led, 45-7, midway through the fourth quarter before safety Benny Barnes returned an Amos Lawrence fumble for 72 of the most unnecessary yards in Dallas history for a touchdown. It was 45-14.

The 49ers also lead the NFC West with the same 4-2 record that the Los Angeles Rams possess.

"We know we've been playing well despite what you've been reading in the press," said San Francisco Coach Bill Walsh, whose team has scored 75 points in the last two weeks (last week the 49ers beat the Redskins, 30-17).

"We saw this coming," said Walsh.

He definitely was in the minority. Quarterback Joe Montana led an offense that gained 440 yards. He completed l9 of 29 for 279 yards and two touchdowns.

"I think everybody was thinking about last year's game against Dallas," said Montana, who was a reserve then and who made the famous Dallas defense look like reserves today. "Anyway, they are America's team, you know."

They certainly weren't today's team. Montana led the 49ers to touchdowns on their first two possessions. He threw a one-yard scoring pass to Freddie Solomon, then watched Paul Hofer run four yards for the second score.

Then late in the quarter Dallas' Drew Pearson fumbled away a Danny White completion on the Dallas six in one of the strangest fumbles you'll ever see. Safety Ronnie Lott nudged Pearson's right arm and the ball bounced toward the sideline, but hit the referee, thereby staying in play for Lott to recover. Four plays later Johnny Davis ran one yard, and it was 21-0.

For the sellout crowd of 57,574 this was football nirvana, the kind usually located on the East Bay with the Raiders. This was the most points ever scored by the 49ers in Candlestick Park.

But the Cowboys are troubled.

White, who completed just eight of l6 for 60 yards and two interceptions, before being replaced in the third quarter by Glenn Carano (three of 12 for 53 yards), glumly analyzed the offense that netted five yards in the first quarter and 192 in the game.

"It will be difficult to find any point in our offense that was successful . . . we have got to be concerned," he said.

Randy White, the defensive tackle of seven years, was more succinct in analyzing the defense that today was more doomed than Doomsday: "They humiliated us. We were very bad."