Senate supporters of the balanced-budget amendment to the Constitution yesterday fended off a series of proposed changes aimed at leaving Congress more leeway to approve deficit spending.

The votes showed that the proponents have a solid majority in the Senate to defeat unwanted amendments but not necessarily the two-thirds needed for final approval.

A time agreement calls for a final vote on the amendment, in its second day of debate, by next Wednesday.

The proponents hope to keep the measure clear of most amendments to make ultimate passage easier if the House concurs.

Meanwhile, House Judiciary Committee Chairman Peter W. Rodino Jr. (D-N.J.), who strongly opposes the amendment, announced that he will hold hearings on the House version next week. His announcement was viewed as a way of both airing the views of opponents and discouraging members from signing a discharge petition to wrest the amendment from his committee and send it to the House floor.

Rodino's committee has held up the amendment for months, a reflection of the House leadership's desire to block it.

The amendment would require Congress to vote balanced budgets each year unless the country is officially at war or unless three-fifths of the members of each House specifically vote to permit a deficit.

The key Senate vote yesterday was on a change that also would have permitted budget deficits when either Congress or the president declared that a national emergency existed. It was defeated 61 to 34.

Its author, Sen. Alan Cranston (D-Calif.), a leader of the opposition, argued that permitting deficits only during war is too restrictive and could prevent an increase in military spending for events less serious, such as regional conflicts.

He called the present language a "straitjacket for national security" that would leave Congress unable to respond with bigger budgets in case of natural disasters domestically.

His proposal prompted an extended tongue-in-cheek colloquy in which Sen. Daniel Patrick Moynihan (D-N.Y.) envisioned an occasion when the president might have to declare war on some foreign country in order to obtain extra funds for domestic purposes.

"I can imagine the State Department forming a planning group already to find some country which would not mind us declaring war on it," Moynihan said. Iceland would be a reasonable choice, he said, except that it would involve trouble with other North Atlantic Treaty Organization countries. Lichtenstein, he added, is not large enough to justify a declaration of war.

Sen. Strom Thurmond (R-S.C.), a leading supporter of the amendment, objected to Cranston's measure on grounds that it would make it too easy for Congress to adopt budget deficits.

Another change permitting unbalanced budgets in times of both war and a "national economic emergency" was defeated 67 to 30. It was introduced by Sen. Alan J. Dixon (D-Ill.), who claimed that without it Congress would be unable to deal with a depression.