A strike against container-loading operations at Atlantic and Gulf Coast ports are threatened last night as shippers and the International Long-shoremen's Association approached a midnight strike deadline without agreement on job-security protections.

Labor and industry officials said a settlement was still possible if a last-minute breakthough came on the job-protection issue. But preparations were under way to shut down all container operations from Maine to Texas at 12:01 a.m. today - an action that could block the unloading of up to 70 per cent of all cargo at some Eastern ports.

ILA President Thomas W. Gleason said earlier that any strike would be a "selective" one, aimed soley at container operations, under which cargoes are prepacked in van-sized steel crates and loaded and unloaded largely by machines.

The union, claiming that the growing use of containers is eliminating jobs traditionally done by dockworkers, is seeking additional pay and benefit protections, including an expansion of minimum-income guarantees from containership-operators.

Although the ILA also wants hourly wages raised from $8 to $10 and a one-year rather than three-year contract, union and industry officials agree that job security is the overriding issue - as it has been in most other major contract negotiations this year.

A selective strike - first used on th docks in a brief ILA work stop-page over the jobs issue last April - would keep many of the ILA's 50,000 Atlantic and Gulf dockworkers on the job handling standard cargo, passenger ships and perishables.

Federal officials said a selective strike also would make it more difficult for the government to stall the strike with an injunction, a tool it has used extensively to block work stoppages on the docks since World War II. With cargo still being loaded and unloaded, proof of impending harm to the nation's economy, as required for an injunction under the Taft-Hartley Act, might be difficult to establish, the officials noted.

The talks were being conducted in New York Between the ILA and the Council of North Atlantic Shipping Association. Representating shippers at ports in Boston, Providence, New York, Philadelphia, Baltimore and Hampton Roads, Va.

But any strike also would affect Southern ports, including huge facilities in Houston, although shippers serving them were not involved directly in the New York negotiations. The ILA is demanding that job protections be applied at Southern as well as Northern ports.

A meeting between representatives of Southern shipping associations and a delegation of North Atlantic shippers was held yesterday in New Orleans in hopes of winning an industry wide accord satisfactory to the union. There was no report from the meeting as of late yesterday.

West Coast ports were also not directly involved because their contracts are with the independent International Longshoremen's and Warehousemen's Union and do not expire until next year. But the 60,000 member ILWU has agreed to abide by picket lines at ILA-targeted container operations on the Pacific coast.

Impetus for new job-security provisions came last year when the National Labor Relations Board, backed by the federal courts, outlawed an ILA contract clause giving union members jurisdiction over handling container cargo within a 50-mile radius of any port. With this job-preservation guarantee gone, the union demanded new ones to protect members from job losses due to increased containerization.