National Football League teams that failed to make the playoffs in 1976 figure to benefit from a proposal that would modify the upcoming league draft.

Under the plan, which has been suggested by an NFL club owner, the first two rounds of the draft would be conducted in the conventional manner.

But on the third round, only the 20 teams that did not qualify for the playoffs would select players. Then the eight clubs with the worst records would pick in the same round.

On the fourth round, only the 20 clubs that did not make the playoffs would pick.

The modification was proposed because the clubs that finished low in the standings may find it tougher to sign players under the new contract.

Regardless of whether the modification is approved, a drafted player must be offered a contract of $20,000 for one year and up to $200,000 for four years on or before June 15.

If a player does not sign, he is eligible for the draft the following year.If he is drafted and still does not sign, he becomes a free agent after another year's time and may sign with any NEL club.

The proposed change, which must be passed by 21 NFL teams, would make the draft more acceptable to the courts, which have held that the original 17-round concept was illegal under antitrust laws.

Meanwhile, some clubs are becoming increasingly concerned that the necessary 21 votes may be rounded up to require team that signed veterans, who played out their options in 1975 or before, pay compensation retroactively.

No compensation was paid to the original employers last year because the so-called Rozelle Rule, or compensation clause, was suspended by the NFL when the clause was ruled illegal under the antitrust laws.

A modified Rozelle Rule has been restored under the new collective bargaining agreement, providing for predetermind compensation with draft choices when a veteran plays out his option.

The New York Giants have volunteered to pay compensation retroactively to the Miami Dolphins for signing option-playout Larry Csonka.

With the new compensation based on the salaries negotiated from the new clubs, the Dolphins conceivably could collect retroactively as many as five No. 1 draft choices for Csonka, Paul Warfield (signed by Cleveland), and Jim Kiick (signed by Denver). Cleveland reportedly also is willing to pay compensation.

The Redskins might have to pay several No. 1 draft choices for signing John Riggins from the New York Jets, Calvin Hill and Jean Fugett from Dallas, Pat Sullivan from Atlanta, and Ernie Janet from Philadelphia.

Retroactive compensation would be complicated because teams like the Redskins do not have draft choices available and veterans may not be exchanged in place of draft choices under the new labor contract.

Consequently, some clubs fear the majority may decide to award compensation from the college pool of players before the regular draft is held. In that case, clubs that are not owed compensation would be penalized by the dilution of top picks available.

An obvious fear is that if the Dolphins or Cowboys were awarded several No. 1 draft choices, they would have big advantages in their divisions, as well as in their conferences.

Eight votes would be necessary to defeat the compensation proposal. Among those already known to be against retroactive compensation are Washington, Baltimore, New England, Oakland and Los Angeles.