House and Senate conferees have resolved one of the most heavily lobbied defense issues of the year by picking the Lockheed C5B as the Air Force's new cargo plane, congressional sources said yesterday.

But the conferees also threw a small consolation prize to backers of the rival Boeing 747 by agreeing to buy three surplus models for $145 million.

The House-Senate conference committee, which acted on the cargo plane controversy late Thursday, continued meeting last night in an attempt to iron out disagreements in a 1983 defense authorization of $177 billion.

The decision to choose Lockheed's cargo plane as the basic long-distance Air Force transport appears to have settled a dispute that had pitted Boeing and its chief congressional supporter, Sen. Henry M. Jackson (D-Wash.), against the White House and the Pentagon.

It will mean multibillion-dollar contracts over five years for Lockheed and a big victory for that company's lobbyists on Capitol Hill and for the Georgia delegation. The decision Thursday would authorize about $800 million for the first of 50 planes to be delivered in the next five years, the sources said.

Jackson said yesterday that spending $145 million to buy three Boeing 747 jumbo jets, which are made in his state, was a "major accomplishment." He predicted that the Pentagon may buy others after using the first three.

However, the Pentagon has said it cannot use the 747s and, if required by law to purchase some, will dole them out to the Air National Guard and reserve units.

The House defense authorization bill had earmarked the money for Lockheed planes, but the Senate, pressed by Jackson, had opted for the Boeing model.

Meanwhile, in a separate conference committee, the Pentagon lost two rounds when conferees on 1982 supplemental appropriations deleted startup construction funds for the MX missile nuclear warhead and an enhanced-radiation (neutron) artillery shell.

House conferees bowed to their Senate counterparts in both cases. Deleted were $7.5 million sought for tooling facilities for the 155-mm neutron artillery shell and $20.9 million to begin tooling up for the MX warhead.

The neutron shell is part of the planned deployment of neutron weapons in Europe. The Pentagon already had been granted $15 million for it in the regular 1982 appropriation for work at five production facilities in the United States.

Committee sources said the MX warhead money was dropped in part because of the narrowness of the recent House vote that approved the missile. The Senate had disapproved expenditures for both weapons when it considered the supplemental, and the House had approved both. They will be reconsidered for the fiscal 1983 authorization.

The defense conferees also set aside a House restriction and agreed to let the Pentagon proceed to produce nerve gas. They also sided with the Pentagon and overrode the Senate to provide funds to build the first MX missiles.