The Reagan administration's 1983 budget will propose more than doubling the level of regular military assistance to El Salvador, State Department sources said last night.

A sizable increase in conventional economic aid to that Central American nation also is proposed. Those increases, together with a new program for several Caribbean nations, could bring the total aid package for El Salvador to more than $300 million.

The increases reflect the administration's plan for staving off an insurgent takeover, despite growing congressional concern about a prolonged commitment that might include using U.S. forces.

Assistant Secretary of State Thomas O. Enders yesterday reiterated on Capitol Hill the administration's position that "nothing has been ruled out" in connection with its determination to save El Salvador from a takeover by insurgents believed led by communists.

Asked by Sen. Paul E. Tsongas (D-Mass.) if there is any limit on how much money the administration is willing to spend, Enders said no one has set a ceiling. When Tsongas suggested that future aid programs for El Salvador might come to $1 billion to $2 billion and involve the commitment of U.S. forces, Enders replied: "Nothing has been ruled out, but nothing like what you say has been ruled in." It would depend on political and economic developments in that country, Enders added.

The regular military assistance program for El Salvador amounts to $26 million this fiscal year. And administration sources said that would rise to $60 million under the new budget. The actual spending this fiscal year will be about $81 million because President Reagan has promised an emergency component from military stockpiles amounting to $55 million.

Regular economic assistance to that country this year is about $144.3 million, and that would be increased to $165 million in fiscal 1983, the sources said.

El Salvador also is expected to receive another large economic aid infusion--of about $100 million --from the administration's Caribbean Basin Initiative, still to be unveiled. If an amount of that size is included for fiscal 1983, it would push the total aid program for El Salvador to more than $300 million.

Congressional concern about the growing U.S. commitment was evident yesterday when Enders testified before the Senate Foreign Relations Committee. Several members from both parties told him that constituents are increasingly asking what the United States intends to do with regard to El Salvador.

Sen. Larry Pressler (R-S.D.) said businessmen in his state were upset by the growing U.S. commitment and he suggested a special presidential address on the issue.

Sen. Nancy L. Kassebaum (R-Kan.) said she feared a continuing military stalemate or new escalation unless negotiations can be arranged between the civilian-military junta and rebel groups.

"Can you see light at the end of the tunnel?" she asked, using a description earlier administrations had applied to the Vietnam war.

"I'm fundamentally on the optimistic side," Enders said. "This government has come a long way."

Enders said that Salvadoran government forces need to be strengthened to resist armed insurgents and preserve the country. "It's going to take more than is now being provided" in order to protect the country while a new political process runs its course, he said. "More, yes . . . , but not so much more that you have enough to physically exterminate the rebels."

He later estimated the government forces at 13,000 and armed insurgents at 5,000.