The Christmas-treed highway bill finally approved yesterday by the Senate means that Santa Claus will be toting a $1 million gift arranged by Rep. Robert A. Roe (D-N.J.) for ailing businesses in Wayne, N.J., his home town.

Roe's unusual gift will take the form of payments to several businesses that say their sales have been hurt by traffic jams stemming from a nearby federal highway construction project.

Congressional sources said Roe was so adamant that he and other House conferees who met with their Senate counterparts to hash out differences this week indicated that there could be no final bill without the Roe amendment.

"It's sensitive," said a high official at the Department of Transportation. "I don't know if it is a precedent, but it's rather unique. We won't know the implications until we look into it."

The House conferees, taking an equally hard line, also overrode Senate objections and authorized an unusual $3 million study of national public-works needs, apparently to be carried out by a firm in the district of House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.).

Senators who argued against the study contract reportedly were told that O'Neill was insistent that the provision be in the final version of the highway bill. The legislation skirts normal contracting procedures and directs that the study be done for the House Public Works Committee with funds provided by the House Administration Committee.

Sources indicated that the vaguely defined study would be done by Abt Associates, a consulting firm in Cambridge that frequently does contract work for the federal government. Yesterday an Abt official and an O'Neill aide expressed puzzlement at the reports and promised to check them out and report back, but neither did so.

The "infrastructure study," as it is called in the bill, will involve "design and preparation of a National Public Works Inventory and Assessment and a preliminary analysis of relevant, existing data."

Roe's proposal was considered unusual in several respects. It sets no qualifying standards for distribution of the federal money; it allows the funds to go to businesses in "the general vicinity" of the highway-widening project, and it establishes what Senate conferees called "a bad precedent" -- perhaps opening the door for businesses in similar straits elsewhere.

Among the businesses affected by the Wayne highway project is a contracting business run by Roe's brother, James, who maintains an office in the complex of stores and eateries. Rep. Roe could not be reached yesterday, but an aide said the congressman's brother would benefit in no way from the legislation.

"This is not any kind of boondoggle," said Robert W. Maitlin. "There is no interest in this for the congressman and it is completely unfounded that his brother would benefit. . . . Mr. Roe is a congressman. He represents these people; he wants to help them."

Maitlin said that businessmen in the area, where Roe also maintains a district field office, had written letters and visited Washington in unsuccessful attempts to get some kind of federal help for their afflicted shopping area.

"Several have gone out of business, and sales are off 60 to 70 percent in some cases, and the store owners say it is because traffic has been rerouted onto their street while the highway-widening project continues," Maitlin said.

"This project will go on until 1984. Mr. Roe thinks they deserve federal help because the problem is created by a federal project."