The White House yesterday signaled concern about continuing Israeli military action in Lebanon by raising doubt whether the planned meeting Monday of President Reagan and Prime Minister Menachem Begin will take place.

Government officials who had previously indicated the meeting was definite began describing it as tentative.

The administration also decided to defer the formal notification to Congress of a planned $2.5 billion sale of F16 warplanes to Israel.

These signals of administration concern were made public in low-key fashion at the White House and the State Department, where they were described by official sources as efforts to put Israel on notice about the consequences of a military strike into heavily populated Beirut.

In another action, the administration decided to support short-term renewal of the U.N. peacekeeping force in southern Lebanon, even while continuing to explore more extensive arrangements to ensure Israeli security and thus obtain the withdrawal of Israeli troops.

The possibility of sending U.S. troops as part of a new force in Lebanon was given a setback by a negative statement from Senate Majority Leader Howard H. Baker Jr. (R-Tenn.). He told reporters at the White House, following a briefing on Reagan's recent trip to Europe, that he does not favor such a new U.S. military involvement in the Middle East on any basis and "certainly not as the lead" of any Lebanon peacekeeping force.

Baker expressed essentially the same view earlier to Israeli Ambassador Moshe Arens, according to a Baker aide.

On Monday, U.S. officials said no decision had been made on whether to back continuation of the 7,000-man U.N. peacekeeping unit, which Israeli forces bypassed in their invasion of Lebanon. Early yesterday, however, the U.S. mission to the United Nations was instructed to support a one-month to six-month renewal of the force's mandate, which is to expire Saturday.

State Department spokesman Dean Fischer, announcing the U.S. decision, said it is "prudent" under existing circumstances to extend the life of the U.N. unit. "Its mandate must not be allowed to lapse at this critical juncture," he said.

The administration is reported to be still at an early stage of discussion, to say nothing of decision-making, about political and military arrangements in Lebanon to bring about Israel's withdrawal and long-term stability there. Officials said much depends on the findings of special U.S. envoy Philip C. Habib, who was in Beirut yesterday discussing these issues.

On Capitol Hill, 38 senators called for the withdrawal of Israeli and Syrian forces from Lebanon, a strengthened Lebanese government and curbs on the Palestine Liberation Organization. Heading the list of 22 Democrats and 16 Republicans were Democratic leader Robert C. Byrd (W.Va.) and Bob Packwood (R-Ore.).

The primary focus of attention at the moment, administration officials said, is the continuing military confrontation in Lebanon, especially the possibility that Israel will go beyond its encirclement of Beirut to seek to capture or kill Palestinian forces within the city.

While saying almost nothing in public about the attacks on Beirut, the administration is reported to have raised the issue on an urgent basis with Israel on several occasions in recent days.

Israeli Radio reported that Habib appealed to Begin Sunday night to stop the bombing of Beirut. The report quoted Habib as saying that Israeli attacks there were out of proportion to cease-fire violations by Palestinians.

Secretary of State Alexander M. Haig Jr. was quoted in the same report as telling Arens in Washington that "continued bombing of Beirut would destroy what remains of the goodwill of your friends in the United States."

The decision to display modest public signals of concern, according to official sources, was made at the White House with the concurrence of Haig. It was implemented by having White House and State Department spokesmen tell reporters of the "hope" that a Reagan-Begin meeting would occur Monday, and to describe that meeting as "tentative."

No such conditional language was used on May 26 when the White House announced Begin's visit. The prime minister left Israel for New York yesterday to attend the U.N. Special Session on Disarmament.

The decision to sell 75 more F16 warplanes to Israel was announced by the administration May 26, during the visit here of Defense Minister Ariel Sharon. Congress was informally notified under a timetable that normally would have led to a formal notification last Monday.

Official sources indicated that the notification is being temporarily withheld partly in order to add to the "signal" to Israel, and partly because of the possible Arab reaction to new warplane sales while Israel is using U.S. aircraft in its invasion.

U.S. planes, tanks and other weapons are supplied to Israel under an agreement that they will be used only for "defensive purposes." The administration has said it is studying whether the Lebanon invasion qualifies.