House and Senate conferees reached agreement yesterday on a record $52.9 billion weapons authorization bill that adds almost $6 billion more for military hardware and research than President Carter requested, plus an additional $1 billion for a military pay increase.

The measure also includes a strongly worded recommendation to Carter or his successor that the development and production of a new strategic bomber to replace the aging B52 be "vigorously pursued."

The conference committee included $375 million for work on a new bomber, several times what the Pentagon had asked for, so that a selection among various options could be made by March 15, after the election, and the new craft could be in the air by 1987.

The committee action, in effect, wound up compromising between a $51.9 billion measure passed by the Senate Armed Services Committee and a $53.1 billion measure passed by the House committee.

The compromise measure, which now goes to the House and Senate for approval, covers authorization for weapons, research and development for fiscal year 1981, beginning Oct. 1.

When the bill eventually gets to the president's desk, Carter will be confronted with a figure almost $7 billion above the one he sent to Congress earlier this year.

The billion-dollar pay increase would provide an 11.7 percent raise in basic pay, subsistence and quarters allowance, effective Oct. 1.

Fifteen other items in the bill, either new or for which funding has been increased, relate to pay and benefits. These include increases in enlistment and reenlistment bonuses for active and reserve personnel, and increases in per diem allowances -- measures intended to stop the flood of personnel from the military because they cannot afford to stay.

The conferees also authorized 2,900 more troops for the Marine Crops than the Pentagon has asked, which would raise the Crops' strength to 188,100.

The committee, reflecting growing concern over the quality of the all-volunteer force, also ordered restrictions that would limit all services to taking no more than 25 percent of their recruits from the lowest acceptable mental category in fiscal 1981 and 1982 and 20 percent thereafter. It also would restrict the number of Army recruits who are not high school graduates to 35 percent next year.

In other bill highlights:

The committee agreed to provide $35 million for the CX transport plane, which the president says is necessary to shuttle equipment abroad, but only if the Pentagon can first prove that the plane can do the job. The House had provided no money for the controversial new aircraft.

The conferees agreed to accept a Senate proposal to take extra Minuteman III intercontinental-range missiles out of storage and deploy them, but cut the number and initial money in half from the 100 missiles and $10 million it originally proposed.

The committee included $285 million for eight new SL7 cargo ships that the Senate wanted. These are meant to help speed equipment to trouble spots abroad in the president's new rapid deployment force.

The lawmakers also appeared to soften language in an earlier Senate bill that would have restricted initial deployment of the big, new MX missile to half the 200 units the Pentagon wants to put in Utah and Nevada.

The conference bill says the full system can be deployed in those two states if, after a study by the secretary of defense, it is determined by Congress that deploying the missiles in other states would be too costly or otherwise difficult.

Reflecting growing congressional concern over the readiness of U.S. forces, the committee also approved a provision that would require authorization of operation and maintenance funds, money that now requires only appropriations action.