The Miami Dolphins have a ready defense for not taking newly profiled running back Leroy Harris until the fifth round of the draft, as their second pick: they were desperate to draft at other positions because of injuries.

Why the rest of the teams in the National Football League did not select Harris, from Arkansas State before then, the Dolphins profess not to know.

Harris, who seized on Monday night's national telecast to rise to prominence with a 77-yard touchdown run from scrimmage that put away the Baltimore Colts, was reminding people that he had done the same thing before he came up to the pros.

"A lot of my best runs in college were against the grain (as against the Colts), where I cut back on my own, when it was not designed.

"With my weight (220) in making that kind of a cutback, the only kind of tackle people can make is an arm tackle. As large as I am, an arm tackle can't bring me down."

The Dolphins' press brochure, published before the season, offers evidence that the Miami scouting department had solicited first-hand information on Harris. Coach Bill Davis is quoted as rating Harris, "The greatest big-play man in Arkansas State history."

Bobby Beathard, Miami's player personnel director, is on record in the brochure as saying he was impressed by Harris' powerful leg drive and "exceptional balance . . . and he can really take a hit."

That's exactly what Harris did Monday night, as first 243-poung defensive end Fred Cook clutched him at the line of scrimmage and then defensive backs Norm Thompson and Lyle Blackwood to no avail.

Beathard rated Harris as the best college fullback in the county and had to live with that until Harris began to produce three games ago.

A year ago, Beathard had running back Gary Davis of Cal Poly "rated with Archie Griffin (of Ohio State), Honest." Beathard had to bear with the skepties with that assertion, too, until Davies ran for 104 yards in the 55-14 devastation of St. Louis Thanksgiving Day.

The Dolphins had to draft linemen on the first and second rounds after their players, mostly on defense, had 11 knee operations in 1976. Miami took A. J. Duhe of Lousiana State and Bob Baumhower of Alabama and those two are starting at the defensive ends.

Coach Don Shula insisted on taking an offensive tackle on the third round in hopes of making quick repairs, so Mike Watson of Miami (Ohio) was selected. Because placekicker Garo Yepremian had been playing for 10 years and punter-running back Larry Seiple for 11, placekicker-punter Mike Michel of Stanford was drafted and is doing the kicking off and punting.

Beathard got his way with Harris on the fifth round, after Detroit, Buffalo, the New York Jets, New York Giants, New Orleans, Philadelphia Atlanta Pittsburgh, Houston and Green Bay passed him up in that round.

Yet, as a senior, Harris led the national with an average of seven yards a carry on 150 attempts for 1.046 yards. He had eight 100-yard-plus games and 13 touchdowns, one of them and 85-yard burst from scrimmage. He had a 207-yard rushing game as a junior.

Harris already had convinced the Dolphins he is an exceptional receiver at full speed, something at which fullback Larry Csonka was not so proficient. Csonka caught 32 passes over a four-year span.

Certainly, Harris and running mate Davis have more speed than Csonka and Jim Kiick did.

Harris sat on the bench for five games in this his rooke year, as had another rookie named Harris, Franco of the Pittsburgh Steelers.

Franco still ended up with 1,000 yards after seven games of 100 or more in his first year.

Meanwhile, Shula confirmed he snuabed Baltimore Coach Ted Marchiabroda after the Dolphins' 17-6 win over the Colts Monday night because of disagreements between the two.

After the game, Marchibroda came trotting over to Shula to congratulate him. Shula waved him off and turned away.

"I knew it was him and I brushed him off," Shula said yesterday.

The Shula-Marchibroda dispute goes back to the first Dolphin-Colt game this year when linebacker Stan White told Marchibroda that Shula was laughing at the Colts while holding a 28-10 lead. It was later reported Marchibroda used that to motivate the Colts in their eventual 45-28 victory.

Although Shula emphasized yesterday he didn't want to make any big deal of the Monday incident, he said, "I felt it was a cheap way to motivate the team, if that's what he was trying to do."

Shula has explained before that he did laugh but that it was because White seemed to think he was yelling at him during the game, when he was really shouting at an official. "I said 'No, no, not you, Stan'" and chuckled briefly.