President Reagan's plan for basing the MX missile system drew stinging rebukes yesterday from two leaders of his party who will play key roles in steering the proposal through Congress.

Sen. John G. Tower (R-Tex.), chairman of the Senate Armed Services Committee, said the system is "enormously vulnerable" to Soviet attack and pronounced himself "gravely disappointed" with the president's decision.

On the House side, Rep. William L. Dickinson (R-Ala.), ranking minority member of the Armed Services Committee, said he was pleased with the president's decision on the B1 bomber but "surprised, disappointed and disturbed" at the MX proposal.

Congressional reaction to yesterday's announcement was by no means one-sided, however. Senate Majority Leader Howard H. Baker Jr. (R-Tenn.) predicted that the plan will be approved by Congress basically in the form it was presented.

His House counterpart, Rep. James C. Wright Jr. (D-Tex.) was supportive of the plans to develop and base the MX missile, but he objected to the decision to build 100 B1 bombers at a cost of $200 million apiece, saying the planes cost too much and could not be produced until 1986.

Many congressmen choose to give a half-and-half review of the president's strategic package. "The MX in silos is a very good idea, the B1 is a turkey," said Rep. Les Aspin (D-Wis.), putting the matter as succinctly as possible.

Of all the members of Congress who issued statements yesterday, Tower appeared the most exercised about the plan.

"The president's specific program for basing the new MX missile only places a more lucrative target in already vulnerable fixed silos and in a configuration which is not particularly useful for ballistic missile defense," he said in a statement.

Later, in response to a question at a news conference, Tower said that the president had "just opened that window of vulnerability wider." He added: "This kind of system gives us no bargaining leverage at all with the Soviets . . . . It's certainly not an incentive to arms talks."

Tower said he has already asked Sen. John W. Warner (R-Va.), chairman of the subcommittee on strategic forces, to conduct detailed hearings as soon as possible.

Warner, who announced that hearings will begin Monday, issued a statement supporting the proposals, saying they sent a "clear signal" to the Soviet Union of this country's determination to "restore the balance in the strategic warfare area."

Elsewhere on the Hill yesterday, reaction varied:

* Sen. Strom Thurmond (R-S.C.), another Armed Services Committee member, called the plan "a positive step."

* Sen. Orrin G. Hatch (R-Utah), whose state had been under consideration as a site for the mobile MX system, said the president's decision would "show our allies in Europe that we are not weakening."

* Sen. Howard W. Cannon (D-Nev.), who also opposed the plan to build multiple shelters in his state, said he would back the Reagan proposal if assured that "it was made for the nation's security and not political reasons."

Sen. J. James Exon (D-Neb.) was a good deal more forceful with his suggestion that politics was at the root of the president's decision. "The president has adequately responded to his political base in the West and to the wishes of his friends in the Mormon Church, but I am not certain his program satisfies our critical defense needs," said Exon, who is a member of the Armed Service Committee.

But Majority Leader Baker said he was sure the president's decision against basing the MX in the Southwest "had nothing to do with politics, nothing to do with geography and certainly nothing to do with friendship."

* Rep. Samuel S. Stratton (D-N.Y.), a member of the House Armed Services Committee, said he considered the B1 decision a "good one" but the MX decision a "mistake."

* Rep. Bill Alexander (D-Ark.) backed the decision to put the MX into Titan silos, some of which are located in his state. He said replacement of the Titans was "long overdue" and that they were "obsolete. . . bordering on dangerous."

* Sen. Edward M. Kennedy (D-Mass.) said it was a "serious mistake to revive the discredited and extravagant B1 bomber." He praised Reagan for rejecting the racetrack basing proposals for the MX, but went on to criticize his proposal to place the missiles in fixed, hardened silos, arguing that it did not address the issue of vulnerability.