LTV Corp. announced today a $450 million takeover bid for Grumman Corp., a move that would make the combined company the nation's seventh largest defense contractor.

Grumman said the LTV offer was unsolicited and that its board of directors would meet promptly to consider the legal and antitrust implications of the bid. Grumman Chairman John C. Bierwirth urged Grumman shareholders in a statement "not to act hastily" on any LTV offer.

LTV, an energy, steel and aerospace company with 1980 sales of $8 billion, is itself a major Pentagon supplier. Grumman last year sold the Pentagon about $1.3 billion of planes, including the F14 fighter, and other equipment and services -- nearly 75 percent of its total sales of $1.76 billion.

A combined Grumman-LTV corporation would be tied with Hughes Aircraft Corp. for seventh place on the Pentagon's defense-supplier list. General Dynamics Corp. is the leading defense contractor, with sales of $3.5 billion last year.

Defense Secretary Caspar Weinberger told the House Budget Committee he would watch carefully the proposed merger to make sure that the nation's defense interests were not compromised.

Grumman gained notoriety last year when its new "Flxible" buses developed metal fatigue after only several months of service. Grumman recalled the buses from major cities such as New York and Chicago to reinforce the undercarriages.

Nearly all Grumman's other sales are in aerospace -- it makes four Navy planes and one Air Force plane, the EF111 -- and in special vehicles.

LTV owns Jones & Laughlin Steel, the nation's third-biggest producer, and is a major energy company as well. It proposes to merge its aerospace subsidiary, Vought Corp., with Grumman and move Vought's headquarters to Bethpage, Long Island, N.Y.

Paul Thayer, chairman of LTV, said in an interview that the Dallas-based conglomerate first began to look seriously at Grumman about a month ago. Last Monday, Thayer said, he called Bierwirth to discuss a merger. Bierwirth was out of town, and he talked instead to the company's president, Joseph G. Gavin Jr., who called Thayer back to tell him that Grumman was not interested in a merger.

"I advised him that I was in a position to make a tender offer a direct offer to Grumman shareholders with or without the consent of Grumman's directors . His response was 'So be it,' " Thayer said. The chairman of the $8 billion LTV company said he still hoped the merger could be accomplished on a friendly basis -- that is, with the acquiescense or approval of the Grumman board of directors.

LTV is offering to pay $45 a share for about 10 million shares of Grumman, roughly 70 percent of the outstanding common stock (including some securities that can be converted to common stock). Its offer is contingent upon receiving at least 50.01 percent of the outstanding Grumman stock.

As often seems to happen in major acquisitions, word of LTV's interest in Grumman apparently leaked out late last week, according to Wall Street insiders. Trading in Grumman, which averaged less than 10,000 shares a day for the first three days of last week, spurted to 61,300 shares on Thursday and 44,500 shares on Friday.

On Monday, 102,200 shares changed hands, and on Tuesday, the day before the offer, volume climbed to 286,000 shares. Grumman, which traded in the $22-a-share range for the first three days of last week, climbed steadily after that to close at $26.75 Tuesday.

Trading in Grumman was suspended today until about 2:45 p.m., when 101,000 shares were bought for $36 a share. Grumman closed the day at $35.875 a share, up $9.125. LTV closed down 75 cents to $15.50.

The New York Stock Exchange said it is examining trading in both Grumman and LTV stock, as it routinely does after a major news announcement such as a merger proposal.

LTV has been casting about for an aerospace merger for some time. Earlier this month it dropped a bid to acquire the Boston-based aerospace company Pneumo Corp. for $180 million after Pneumo directors rejected the bid as inadequate.

Thayer said there is an "excellent fit" between Grumman and LTV. LTV is a major supplier of missiles and electronic equipment, while Grumman's strength is in aircraft, an area LTV de-emphasized a few years ago in favor of missiles. merger for some time. Earlier this month it dropped a bid to acquire the Boston-based aerospace company Pneumo Corp. for $180 million after Pneumo directors rejected the bid as inadequate.

Thayer said there is an "excellent fit" between Grumman and LTV. LTV is a major supplier of missiles and electronic equipment, while Grumman's strength is in aircraft, an area LTV de-emphasized a few years ago in favor of missiles.