The battle, or at least a skirmish, over congressional moves to deny veterans' benefits to servicemen whose undesirable discharges are upgraded under President Carter's program is expected to begin this week.

Congressional opposition to the program has been building since it was announced by Defense Secretary Harold Brown on March 28.

Bills have been introduced in both houses to bar benefits to participants in the discharge upgrade program, and the halls of Congress (or at least the pages of the Congressional Record) have echoed with denunciations of the President's intentions.

Chairman Ray Roberts (D-Tex) of the House Veteran's Affairs Committee has scheduled hearings of a special select committee for June 20-21 to examine the Carter program.

Roberts has expressed his support for a bill that would deny benefits to those whose discharge is upgraded from undesirable to general. About 160,000 are eligible to be considered for such an upgrade.

Rep. Robein L. Beard Jr. (R-Tenn.) doesn't want to wait for hearings or the separate bills, however, and has notified his colleagues that he will introduce an amendment to the Housing and Urban Development independent agencies appropriations bill barring the Veterans Administration from using any funds for benefits to participants in the Carter Program.

That bill is expected to come up early this week.

The White House was looking toward the Roberts hearings as an opportunity for Defense Department and Veterans Administration officials to explain the program.

"It is not a radical program," Margaret McKenna, deputy counsel to the President, said."I think if the program were better understood there would be less opposition."

An aide to Beard said that when the congressman mentions the program to his constituents many of them "are shocked and horrified."

"That these individuals [men receiving upgrades] should be provided with full benefits is simply a slap in the face to those men and women who have served this country honorably," Beard said in his letter.

Carter says he believes this argument misses a fundamental point.

The guidelines that were adopted for the special Carter program were in existence already, McKenna said. All the Carter program does is speed up a process that was already available for men with undesirable and general discharges.

For example, Beard's letter expresses opposition to upgrading discharges of drug offenders. In 1971, then Defense Secretary Melvin R. Laird began a discharge review procedure under which men's discharges were upgraded if their only problem had been drug abuse.

'If the Beard amendment were approved," McKenna said, "people who applied in (Carter's) program would be discriminated against." Those who appealed to discharge review boards outside the Carter program would still be eligible for benefits if they succeeded in having their undesirable discharges upgraded to general or honorable.

In addition to the emotional issue of benefits becoming available to people who formerly held undesirable discharges, members of Congress question the administration's estimate that the program will cost $100 million.

Some members of Congress believe that is a substantial understatement of the full cost and are seeking explanations of now the figure was calculated.