President Reagan warned tonight that "the Soviet-Cuban-Nicaraguan axis" could "take over Central America" if Congress refuses more military assistance for Central American nations friendly to the United States.

"We must not listen to those who would disarm our friends and allow Central America to be turned into a string of anti-American Marxist dictatorships," the president said at a Republican fund-raising dinner here.

"The result could be a tidal wave of refugees--and this time they'll be 'feet people' and not 'boat people'--swarming into our country seeking a safe haven from communist repression to our south," he said.

Reagan's tough talk about what he sees as the communist threat to the region came after he met at the White House today with Richard Stone, his special envoy to Central America, to hear a private report on efforts to achieve a negotiated settlement in guerrilla wars in El Salvador and Nicaragua.

At the meeting, according to a White House official, Stone was told that the United States is not interested in allowing leftist Salvadoran guerrillas to share power while they are in armed revolt against the U.S.-backed government there.

The official said Stone emphasized that the administration should "support the political process" in Central America, including the initiative by the Contadora group composed of Colombia, Venezuela, Panama and Mexico. That group seeks withdrawal of foreign troops from Central America and has offered to mediate between government and guerrillas in El Salvador and Nicaragua. The proposal has made no headway because of disagreement on how to proceed on an agenda.

Aboard Air Force One between Andrews Air Force Base and Jackson, White House spokesman Larry Speakes said the administration has "always favored a dialogue" with all factions in El Salvador. He declined to comment on Democratic presidential candidate Walter F. Mondale's statement Sunday that "it is inevitable that American troops will be sent into Central America" because Reagan policy there is "failing."

Reagan is to meet at the White House Thursday with Felipe Gonzales, the moderate Socialist prime minister of Spain, who last week characterized U.S. policies in Central America as "more negative than positive." It is believed that Stone and Reagan also discussed this meeting.

While the president spoke tonight with alarm about the Central American situation, he pointed with pride to administration efforts to increase the military budget, a theme he has often stressed before southern audiences. During the decade before he took office, Reagan said, "our military strength was permitted to erode disastrously."

"We promised to turn this threatening situation around," he said. " . . . We've set in place a program to rebuild our defensive capabilities. We are doing our best to keep costs down but, no matter how diligent we are, there is no escaping the fact that providing this country with an adequate defense is an expensive undertaking, especially when you're forced to make up for the irresponsibility of so many past years."

Then Reagan launched into a variation of a theme he often used during the 1980 campaign, saying, "We will not send our brave men and women in the military out to defend us with second-rate weapons and bargain-basement equipment."

He added a sentence to his prepared text to say U.S. soldiers are so finely trained and well equipped that "they won't have to use those weapons because no one will dare tread on us." Reagan also made his customary claims for success of his economic recovery program and again promised to veto legislation that would repeal the 10 percent income-tax cut scheduled July 1.

Reagan spoke before 3,500 persons at the $200-a-ticket annual Mississippi GOP fund-raising dinner, where entertainment included country singer Tammy Wynette and the food featured such regional delicacies as fried catfish fillets and boiled crayfish. He was greeted with thunderous applause equaled by cheers given Mississippi-born Wynette when she sang "Stand By Your Man" and kissed and hugged Reagan.

Conspicuously absent were any remarks by Reagan about the Justice Department's dispatch last week of federal registrars into five Mississippi counties to aid in registering low-income black voters who have complained of persistent discrimination in registration procedures.

The additional registrars were ordered into Mississippi by William Bradford Reynolds, assistant attorney general for civil rights, after he visited the state with the Rev. Jesse Jackson. The action was regarded by administration political strategists as likely to have more impact on moderate and liberal white voters than on blacks, who voted heavily against Reagan in 1980 and are expected to do so if he runs in 1984.

Reynolds' action was unpopular with Mississippi Republicans. On Air Force One, Rep. Trent Lott, whose district includes Jackson, said he was "disappointed" that Reynolds did not call William W. Franklin, the state's other GOP congressman, before traveling in the state. Lott also criticized Reynolds' decision to send federal registrars to Leflore County, where Lott said 18,000 of 20,000 potential voters are registered.

Lott was honored by Reagan as representing "all that is best" among new GOP leaders.