The Carter administration yesterday vigorously opposed a series of congressional tax-incentive plans intended to spur exports, arguing the measures would cost the Treasury too much and undermine the new multilateral trade agreement.

In testimony before a Senate Finance subcommittee, Emil M. Sunley, deputy assistant secretary of the Treasury for tax policy, said the measures "would seem to violate the spirit, and perhaps the letter" of the new trade pact.

Sunley dismissed one of the proposals as "unwise" and another as "undesirable tax and economic policy." He said the measures, some of which are similar to existing programs, "can be expected to have . . . limited effectiveness."

Despite Sunley's strong language, the administration's opposition did not seem likely to deter the subcommittee, some of whose members are among the chief sponsors of the new export-incentive proposals.

The subcommittee also heard from a bevy of spokesman from business and trade groups, who contended the tax breaks were needed to help boost productivity, create more jobs, trim back inflation and sell more abroad.

The series of proposals, sponsored in various forms by Sens. Lloyd Bentsen (D-Tex.), John H. Chafee (R-R.I.) and John C. Danforth (R-Mo.), would provide faster depreciation writeoffs for business and tax breaks for research.

Treasury estimates show Chafee's proposal would drain $2.7 billion from government coffers in 1980, soaring to $10.7 billion by 1984. Bentsen's major plan would cost $1.3 billion next year, while Danforth's would cost $1.9 billion.

The Treasury's opposition yesterday put the administration and Congress on what could prove to be a collision course on the question of new investment incentives. Carter is said to favor some new tax plans, but wants the budget held in check.

At the same time, Congress appears to be becoming more and more interested in enacting new tax breaks to spur business investment. Bentsen said yesterday he thought many of the proposals had a good chance of enactment this year.

The proposals the subcommittee began considering yesterday include:

A Bentsen plan to allow businesses to shorten their writeoff of new equipment by 30 percent below the official "guideline life" for that item, instead of 20 percent as under present law.

Chafee's proposal to replace the present system of depreciation allowances with a single cost-recovery period with sharply reduced record-keeping requirements. Most depreciation periods would be cut below 7 years.

A Danforth bill to allow businesses a 10 percent investment tax credit for research and development. Danforth also is sponsoring a special tax credit for business contributions to basic research projects.

A joint Bentsen-danforth plan that would allow special deductions for unrealized foreign currency losses connected with export efforts, a "bad debt" deduction and special treatment for research and development expenses.