Wildcat walkouts against a proposed new contract for postal workers dwindled yesterday, but the pact faced possible trouble on another front.

As nearly normal operations were resumed at walkout-plagued bulk mail centers in California and New Jersey, a rank-and-file bargaining advisory committee of the American Postal Workers Union was reported divided over whether to approve or reject the contract offer.

One source described the outlook as "50-50." Rejection, or even a close vote, could severely complicate chances for rank-and-file ratification of the contract next month.

The tentative contract, providing for wage and cost-of-living increases of 19.5 percent over three years and retention of a contested "no-layoffs" guarantee, was negotiated last Friday between the Postal Service and four unions representing more than 550,000 postal workers. It is subject to approval by a majority of each union's members in referendums over the next couple of weeks.

But the constitution of the APWU, which represents postal clerks and is the largest of the four unions, calls also for a cote by a 49-member bargaining advisory committee composed of appointees of the union's executive board.

The constitution is unclear, however, on whether the group can block ratification.

The committee recessed without a decision late yesterday and was scheduled to resume today.

Union officials indicated they plan APWU's nearly 300,000 members even ned to submit the contract to the if the committee rejected it.

But the dispute could result in litigation, and an adverse vote, whether legally binding or not, could give strong encouragement to the contract's foes, who are challenging the proposed wage rates as well as other provisions.

The union's executive board voted 30 to 15 to recommend ratification of the contract last Friday but scattered opposition has emerged since then - expecially, as expected, in the New York area.

The New York regional APWU branch has sanctioned a strike vote by its 23,000 members of Monday, and the local letter carriers union, representing another 7,000 workers has said it would go along with the vote.

Strikes are illegal, but eight years ago a wildcat strike that started in New York spread to more than 200,000 workers. A difference this year is that the Postal Service has vowed to fire and prosecute strikers and about 70 have been dismissed so far.

While local union officials or rank-and-file groups in several cities from Baltimore to Portland, Ore., have recommended rejection of the contract, wildcat protests subsided at the bulk mail centers, where dissension has been most severe.

The Postal Service said the workforce at the New York bulk mail center located in Jersey City, N.J., was 72 percent of normal, reflecting a gradaul increase from less than 20 percent on Friday. Attendance was also up at bulk mail centers serving San Francisco and Los Angeles.

Postal officials said some delays have occurred in delivering packages and second and third-class mail handled by the bulk centers but added that handling time is now returning to normal. They said delivery of first-class mail has not been affected.

The likely impact of a pro-strike vote in New York next Monday is unclear, although New York union officials have said they expect it would spread nationwide, and officials in Washington and other big cities have said they would be watching it closely.

If the contract is rejected by any one of the unions, the Postal Service and the union could return to the bargaining table or federal mediators could begin proceedings leading to arbitration. Rejection could also lead to localized walkouts or a national strike.