The Air Force may drop its plans to have the first 10 MX missiles deployed and ready for launch by December, 1986, according to Pentagon sources, which means it would no longer need MX production money in the defense appropriations bill for the current fiscal year.

"The Air Force is going to get away from talking about the initial operating date and begin saying instead it must have all 100 MX missiles operational by 1989," a well-placed military source said yesterday.

Air Force vice chief of staff Jerome F. O'Malley denied that a change in the initial deployment date had already been made, but added, "If we do not get a timely basing mode decision" by April, 1983, the initial deployment date will slip.

Because of opposition to the Reagan administration's Dense Pack basing plan, the House voted to delete MX production money from the defense appropriations bill and the Senate Appropriations Committee voted to bar the Pentagon from spending the money until Congress approves a new basing plan.

The Air Force could still have all 100 MX missiles operational by 1989 as planned, military sources said, if the administration and Congress agreed on a basing plan next year and included initial MX production money in the fiscal 1984 defense budget.

This argument has been made by Rep. Joseph P. Addabbo (D-N.Y.) and Sen. Ernest F. Hollings (D-S.C.), who have led efforts to keep MX production money out of the fiscal 1983 budget.

The Carter administration had set the original December, 1986, target date to start deploying 200 MX missiles among 4,600 shelters over a wide area in the western United States. The Reagan administration cut the number of missiles to be built to 100 but kept the date, saying it wanted to close the "window of vulnerability" in which it contended the Soviets had enough warheads to knock out all the U.S. land-based ICBMs.

To meet the December, 1986, operational date, the Air Force intended to begin producing MX missiles while the first flight tests were still taking place. The initial flight test has been delayed at least a month, from Jan. 28 to "sometime in March," according to one source.

A recent failure of the second stage engine of the MX during its fifth test is taking more time to review and fix than reported earlier, according to Capitol Hill sources. Aerojet-General, the contractor on that stage, "is being careful it doesn't happen again," a Pentagon source said.

It will take "18 to 24 months for the first missiles to come off the production line," an Air Force source said yesterday. "After the bugs are worked out, we would expect to build about 48 to 50 a year."

Under that schedule, the Air Force could build the 223 MX missiles needed to support the operation force of 100 by the 1989 target date.

Meanwhile on Capitol Hill, House sources said the MX compromise offered by Sen. Hollings, which would require congressional approval of an MX basing proposal before any MX production funds were to be available, might not be approved. Rep. Vic Fazio (D-Calif.) said he could see a compromise in which the president accepts a version of the House jobs bill and the House accepts the Hollings approach to MX.

At the Pentagon, a senior Defense Department official told newsmen that the administration would mount a major "educational campaign" to gain support for the Dense Pack basing plan so that it will be approved when Congress reconvenes next year.