Rep. Les Aspin (D-Wis.), newly elected chairman of the House Armed Services Committee and a key supporter of the controversial MX missile last year, suggested yesterday that he may now abandon the weapon while supporting the Reagan administration on an anti-ballistic missile (ABM) system.

Aspin, in his first public address since his elevation on Jan. 4, did not commit himself on the MX or any other issue and declined to answer questions on the record after his speech.

But he eased the way for a possible reversal on the MX, which could seriously damage the administration's chances of winning continued support for it. Sen. Barry Goldwater (R-Ariz.), the new chairman of the Senate Armed Services Committee, has already urged President Reagan to give up on the MX.

The 10-warhead MX, 21 of which have already been funded, faces a crucial vote in March that many have portrayed as a first test of Reagan's likely sway over Congress on arms and defense issues generally in his second term. Reagan and other officials have called the MX essential to national defense and U.S. bargaining strength in arms control talks.

Aspin suggested that, since defensive weapons now will be a subject of negotiations with the Soviet Union, the MX may no longer be needed as a "bargaining chip."

"Isn't the threat to build defensive systems around our missiles. . . a more rational threat -- and, therefore, a better bargaining chip -- than the threat to build MX and thereby put at risk their missiles?" Aspin asked. "At least in the former case, the punishment fits the crime. The response would be to defend against the threat, whereas with MX the response is to replicate it."

Secretary of State George P. Shultz and other administration officials have argued that, with the Soviets returning to arms control talks, Congress should strengthen the U.S. hand by funding both MX and antimissile weapons research. During the 13 months when the Soviets boycotted the talks, the administration argued that Congress should fund MX so as not to reward the Soviets for walking out.

Aspin engineered compromises in the Democratic House to keep the MX alive, and yesterday he agreed that Congress should not "send our negotiators to Geneva with a weak negotiating hand." But he said that Congress also should not approve the administration's weapons requests unless it develops and presents a more coherent rationale for its defense and arms control policy.

"Congress is not likely to vote the administration's way on all these issues just because arms talks are going on," he said.

Reagan yesterday congratulated the negotiating team that met with the Soviets in Geneva last week to seek an agreement on resuming talks. He praised the team, comprised of State and Defense Department officials who have sometimes disagreed on arms control policy, for "the unity and the discipline they demonstrated."

But the president warned against "euphoria" now that talks are resuming. "If it isn't a good agreement, if it won't work, we just don't seek a piece of paper," he said.

One member of the team, Richard N. Perle, said yesterday that he "hopes" the Soviets agreed to resume talks in order to reach an accord on reducing weapons. But Perle, assistant secretary of defense for international security policy, told a group of foreign reporters that he is "confident" that another reason for their agreement was their failure to halt deployment of U.S. missiles in Europe by walking out of the talks.

Perle said that a decision now by the Belgian government to delay deployment of American ground-based cruise missiles would be "a serious blow on the eve of the opening" of arms negotiations. But he said that Belgium "has not yet made its decision." There is domestic pressure on the Belgian government not to deploy as scheduled in March, and officials were here in part to discuss the issue this week.

Perle also said that the Soviet position on the relationship between nuclear arms agreements and discussions about space weapons will "only evolve as negotiations take place."

The two superpowers agreed in Geneva to hold negotiations in three forums on strategic nuclear weapons, medium-range nuclear weapons and defensive arms, primarily in space. Since then, they have disagreed about whether progress in one area should hinge on progress in the others.

Perle said that "everyone agrees there is an intellectual linkage between offensive and defensive weapons" but that he hopes there will not be "artificial delays . . .while we wait to see what can be done in other forums" such as space.

He jokingly questioned whether "if we agreed to ban the Strategic Defense Initiative" -- a key Soviet goal -- the Soviets would want to delay signing such a treaty until agreement was reached on offensive nuclear weapons.