Democratic National Chairman Kenneth M. Curtis said yesterday that he expects the party's national committee easily to approve a resolution that "proudly proclaims" its support of approval of the Panama Canal treaties.

Although some opposition is expected from Southern and border states, the endorsement would be in sharp contrast to a Panama resolution voted last week by the Republican National Committee, which condemned the treaties as reflecting "dangerously weak" foreign policy.

Although discussions aimed at giving up control of the canal began 13 years ago, negotiations for the proposed treaties began in earnest in 1974 under the Republican administration, when then-Secretary of State Henry A. Kissinger signed with the Panamanians a declaration of principles.

The Democratic party's resolution cites President Carter's "courageous leadership" in completing and signing the treaties. Carter is to address the party leadership today at is meeting at the Washington Hilton.

In a meeting of the DNC 35-member Executive Committee yesterday, a proposal to add more than 1,000 delegates to the party's midterm conference, schedule for December 1978, received so little backing that it failed to carry even a "straw poll" recommendation to the full committee.

The scheme to expand the so-called mini-convention from 1,627 delegates to 2,783 was a advanced by committee delegations from Georgia and several Midwest states.

It was opposed by Curtis, who said the conference would evolve into a huge political convention-like affair with "all its pitfalls." While he said the major pitfall would be the cost, some Democratic leaders have expressed fears that the liklihood of rancor and the number of resolutions critical of the party and the Carter administration would increase roughly proportionally to the number of delegates attending.

The full committee is to vote on the midterm conference today, along with a spate of other policy resolutions.