A constitutional amendment to ban school busing is expected to be defeated in a vote on the House floor today, despite last-minute attempts by the amendment's supporters to make wording more appealing.

The author of the amendment, Rep. Ron Mottl (D-Ohio), shocked House leaders by getting enough signatures on a discharge petition to bypass the House Judiciary Committee, where the amendment was being bottled up. A majority of the House (218 members) must sign a discharge petition, and a few such petitions are successful.

But things have gone downhill for Mottl and his supporters since their discharge peition forced the issue to the floor. The most damaging setback may have been the refusal last week of the House Republican Policy Committee and the House Republican Conference to endorse the constitutional amendment.

Two factors are responsible for the Republican backoff, one of them political. Rep. Robert McClory (R-I11.) points out that the Republican Party has been seeking to attract blacks to the party, and a vote for the busing amendment "will be interpreted widely as an anti-black vote." McClory said he has talked with Republican National Committee Chairman Bill Brock about it and "he agreed," though Brock has avoided saying anything publicly because of the potential divisiveness of the issue.

The second factor is the wording of the amendment. Mottl's proposal would block assigning children to any school other than the one closest to home. A second sentence says "Congress shall have the power . . . to insure equal educational opportunities for all students."

Some Republicans, such as Rep. William F. Goodling (R-Pa.), a former school official, point out that assignment to the nearest school would prevent busing even if a school became terribly overcrowded.

The second sentence could amount to massive federal intervention in school policies with a result worse than busing even if a school became terribly overcrowded.

The second sentence could amount to massive federal intervention in school policies with a result worse than busing, some Republicans believe.

To deal with those concerns, Rep. Marjorie Holt (R-Md.), with Mottl's approval, will attempt to change the language on the floor. Her wording would make it clear that busing "on account of race, color or national origin" would be prohibited. She also will attempt to do away with language giving Congress the power to insure equal educational opportunities.

Though Holt's language is more appealing, it complicates the parliamentary procedure and underscores the problem of bringing such an intense issue to the House floor with little advance consideration.

Rep. Don Edwards (D-Calif.), leader of the fight against the amendment and chairman of the Judiciary subcommittee that bottled it up, said, "I don't think Marjorie Holt's amendment makes it much better. It indicates what little thought has been given to the drafting of the original amendment. The house floor is not the place to write a constitutional amendment."

Democratic House leaders, the Black Caucus, the American Civil Liberties Unions and other civil rights groups have been aiding Edwards with intense lobbying against the amendment.

But groups such as the National Association Against Forced Busing have been working hard, too, and delegations from cities such as Boston, where busing is in effect, have been making the rounds of congressional offices.